第1套

The Origins of Plant and Animal Domestication

Paragraph 1
The emergence of plant and animal domestication represented a monumental change
in the ways that humans interacted with Earth’s resources: the rate at which Earth’s
surface was modified and the rates of human population growth. The development of
agriculture was accompanied by fundamental changes in the organization on human
society: disparities in wealth, hierarchies of power, and urbanization.

1. The word “monumental” in the passage is closet in meaning to

A. innovative
B. surprising
C. complex
D. enormous

Paragraph 2
Phrases like “plant and animal domestication” and “the invention of agriculture”
create the impression that humans made the transition to cultivating plants and
tending animals rather abruptly, maybe with a flash of insight. Most scholars don’t
think so. It seems more likely that humans used and manipulated wild plants and
animals for many hundreds of thousands of years. The transition to gardens, fields,
and pastures was probably gradual, the natural outgrowth of a long familiarity with
the environmental requirements, growth cycles, and reproductive mechanisms of
whatever plants and animals humans liked to eat, ride, or wear.

2. According to paragraph 2, phrases such as “plant and animal domestication” and

“the invention of agriculture” encourage which of the following wrong ideas?
A. Early farmers were fairly advanced in their knowledge of plants and animals.
B. Agriculture and animal domestication arose as a result of systematic study and
experimentation.
C. The change from hunting and gathering to farming and raising animals occurred
quickly.
D. Early efforts to raise plants and animals were generally successful.

3. The word “manipulated” in the passage is closet in meaning to

A. observed
B. consumed
C. skillfully used
D. protected

4. Which of the sentences below best expresses the essential information in the
highlighted sentence in the passage? Incorrect choices change the meaning in
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important ways or leave out essential information.
A. The change to land cultivation was a slow process because humans were familiar
with the needs of relatively few plants and animals.
B. The cultivation of land occurred gradually as it was the product of extensive
human experience observing plants and animals of value to humans.
C. Gardens, fields, and pastures were outgrowths of the desire for plants and animals
that humans knew from long familiarity were good to eat, wear, or ride.
D. People learned about environmental requirements, growth cycles, and reproductive
mechanisms through their long familiarity with plants and animals that they liked to
eat, ride, and wear.

Paragraph 3
For years, scholars argued that the practices of cultivation and animal domestication
were invented in one or two locations on Earth and then diffused from those centers
of innovation. Genetic studies are now showing that many different groups of people
in many different places around the globe learned independently to create especially
useful plants and animals through selective breeding. Probably both independent
invention and diffusion played a role in agricultural innovation. Sometimes the ideas
of domestication and cultivation were relayed to new places. In other cases the
farmers or herders themselves moved into new zones, taking agriculture or
improvements such as new tools or new methods or new plants and animals with
them.

5. What do genetic studies suggest about the theory that “cultivation and animal
domestication were invented in one or two locations on Earth and then diffused from
those centers of innovation”?
A. The theory underestimates the speed at which cultivation and animal domestication
were diffused.
B. The theory underestimates the number of locations in which cultivation and animal
domestication arose independently.
C. The theory overemphasizes the importance of selective breeding in cultivation and
animal domestication.
D. The theory overemphasizes the importance of cultivation and animal domestication
to some groups of people.

Paragraph 4
Scholars used to assume that people turned to cultivating instead of gathering their
food either because they had to in order to feed burgeoning populations, or because
agriculture provided such obviously better nutrition. It now seems that neither of these
explanations is valid. First of all, the risk attached to exploring new food sources
when there were already too many mouths to feed would be too great. Second,
agriculture did not necessarily improve nutrition or supplies of food. A varied diet
based on gathered (and occasionally hunted) food probably provided a wider, more
secure range of nutrients than an early agriculturally based diet of only one or two
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cultivated crops. More likely, populations expanded after agricultural successes, and
not before.

6. According to paragraph 4, what advantages did the diet of hunter-gatherers

probably have over an early agricultural diet?
A. It required less effort for them to acquire food that was nutritious.
B. It allowed their populations to expand across wider areas.
C. It provided a greater variety of foods needed for them to stay healthy.
D. It allowed them to have more children.

7. According to paragraph 4, what was the most likely relationship between

population growth and food cultivation?
A. Population growth encouraged the development of food cultivation.
B. Population growth was dependent on the development of a varied diet of cultivated
foods.
C. Successful methods of food cultivation were developed before population growth
occurred.
D. Food cultivation was more successful in situations where population growth was
limited.

Paragraph 5
Richard MacNeish, an archaeologist who studied plant domestication in Mexico and
Central America, suggested that the chance to trade was at the heart of agricultural
origins worldwide. Many of the known locations of agricultural innovation lie near
early trade centers. People in such places would have had at least two reasons to
pursue cultivation and animal raising; they would have had access to new information,
plants, and animals brought in by traders, and they would have had a need for
something to trade with the people passing through. Perhaps, then, agriculture was at
first just a profitable hobby for hunters and gatherers that eventually, because of
market demand, grew into the primary source of sustenance. Trade in agricultural
products may also have been a hobby that led to trouble.

8. The word “pursue” in the passage is closet in meaning to

A. practice
B. encourage
C. prefer
D. combine

9. Which of the following most accurately reflects the statement discussed in

paragraph 5, on efforts to cultivate plants and animals?
A. The efforts often failed because hunter-gatherers had limited access to new
information about plants and animals.
B. The efforts were begun out of a desire to produce goods for trade rather than to
increase their growers’ food supplies.
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C. The efforts were sometimes abandoned so hunter-gatherers could become involved
in the more profitable activity of trading.
D. The efforts were not profitable until people began trading food that they had raised
for other goods.

Paragraph 6
E. N. Anderson, writing about the beginnings of agriculture in China, suggests that
agricultural production for trade may have been the impetus for several global
situations now regarded as problems: rapid population growth, social inequalities,
environmental degradation, and famine. Briefly explained, his theory suggests that
groups turned to raising animals and plants in order to reap the profits of trading them.
As more labor was needed to supply the trade, humans produced more children. As
populations expanded, more resources were put into producing food for subsistence
and for trade. Gradually, hunting and gathering technology was abandoned as
populations, with their demands for space, destroyed natural habitats. Meanwhile, a
minority elite emerged when the wealth provided by trade did not accrue equally to
everyone. Yet another problem was that a drought or other natural disaster could wipe
out an entire harvest, thus, as ever larger populations depended solely on agriculture,
famine became more common.

10. Which of the following most accurately reflect the relationship between
paragraph 6 and a topic discussed in paragraph 5?
A. Paragraph 6 discusses a series of events that calls into question the theory that
plants and animals were raised for purposes of trade.
B. Paragraph 6 presents evidence supporting the claim that many sites of agricultural
innovation were located near trade centers.
C. Paragraph 6 identifies problems that led to the raising of plants and animals as the
primary source of sustenance.
D. Paragraph 6 traces negative developments that arose possibly as a result of raising
plants and animals for trade.

11. The word “subsistence” in the passage is closet in meaning to

A. profit
B. surplus
C. enjoyment
D. survival

12. Look at the four squares [] that indicate where the following sentence can be
added to the passage.

Among the many places that are now known to be centers of independent
domestication are Mesopotamia, Central China, and Mesoamerica.

Where would the sentence best fit? Click on a square [ ] to add the sentence to the
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passage.
Paragraph 3
For years, scholars argued that the practices of cultivation and animal domestication
were invented in one or two locations on Earth and then diffused from those centers
of innovation. [A] Genetic studies are now showing that many different groups of
people in many different places around the globe learned independently to create
especially useful plants and animals through selective breeding. [B] Probably both
independent invention and diffusion played a role in agricultural innovation. [C]
Sometimes the ideas of domestication and cultivation were relayed to new places. In
other cases the farmers or herders themselves moved into new zones, taking
agriculture or improvements such as new tools or new methods or new plants and
animals with them. [D]

13. Directions: An introductory sentence for a brief summary of the passage is

provided below. Complete the summary by selecting the THREE answer choices that
express the most important ideas in the passage. Some answer choices do not belong
in the summary because they express ideas that are not presented in the passage or are
minor ideas in the passage. This question is worth 2 points.

Drag your choices to the spaces where they belong. To review the passage, click on
View Text.

Agriculture invention and animal domestication caused lasting changes to how

humans live and to the physical surface of Earth.

Answer Choices

A. The transition from hunting and gathering to raising plants and animals was
gradual and led to significant changes in the organization of human societies.
B. Scholars now believe that agriculture and animal domestication began
independently in many separate locations and then spread to new areas.
C. As trade in agricultural products grew and social inequalities arose, new crops were
developed specifically to feed the labor needed to support societies.
D. Although it is now clear that agriculture developed independently in many places,
often the most efficient techniques arose by combing practices of different cultures.
E. Agriculture became more widespread when human populations realized that an
agricultural diet supplemented through trade could provide as much nutrition as the
hunter-gatherer diet.
F. The earliest reason for raising plants and animals may have been to provide goods
for trade, and such trade may account for the rise in social problems such as
environmental destruction.

Preventing Overgrowth among Tree Branches

Paragraph 1
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One way trees prevent themselves from having too many branches is simply by
shedding (dropping off) branches once they have fulfilled their purpose. This happens
as the tree gets bigger and grows new outer layers of foliage that shade the inner and
lower branches. In most large trees, the center of the canopy contains only large
branches, small branches and fine twigs are found only at the canopy’s edge. In the
shaded center, the small branches that would once have occupied that space are long
gone. Trees like the true cypresses regularly shed small twigs complete with leaves
toward the end of summer. Most other trees shed only branches that prove
unproductive. If a branch is not producing enough carbohydrate to cover its own
running costs—i.e., it needs to be subsidized by other branches because, for example,
it is being shaded and receives little light—it will usually be got rid of. This prevents
unproductive branches from being a drain on the tree and removes the wind drag (the
force of air resistance) from useless branches.

1. All of the following situations are mentioned in paragraph 1 for a tree to shed its
branches EXCEPT
A. endangering other branches
B. building up on a tree
C. wasting a tree’s resources
D. growing larger

2. Which of the sentences below best expresses the essential information in the
highlighted sentence in the passage? Incorrect choices change the meaning in
important ways or leave out essential information.
A. A tree will usually shed branches that use more carbohydrate than they produce.
B. Branches that are shaded usually do not receive enough light to produce all the
carbohydrate they need.
C. If a tree gets rid of a branch, it is usually because other branches lack enough
carbohydrate to subsidize it.
D. If a branch is shaded and cannot produce as much carbohydrate as it needs, it will
usually be subsidized by other branches.

3. According to paragraph 1 most twigs of the true cypresses would be arranged in

which of the following manner
A. Most small twigs on true cypresses have been found located at the margins of the
canopy.
B. The shaded center areas of true cypresses are generally occupied by many small
twigs and branches.
C. True cypresses shed twigs that grow on large, unproductive branches.
D. True cypresses seasonally shed small twigs without regard to whether they are
productive or not.

Paragraph 2
Branches are shed for reasons other than lack of light. In dry parts of the world, it is
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common for trees and shrubs to lose smaller branches to save water. Small branches
have the thinnest bark (the protective outer covering of a tree) and greatest surface
area and thus are the source of most water loss once the leaves have been lost. The
creosote bush of United States deserts self-prunes, or removes parts of itself, in the
face of extreme heat or drought, starting from the highest and most exposed twigs and
working downward to bigger and bigger branches; it’s a desperate act because if the
creosote bush loses too much wood, it dies. Shedding branches can also be useful for
self-propagation. Most poplar trees and willow trees characteristic of waterways will
readily drop branches, which take root when washed up on muddy banks further
downstream.

4. Which of the following best describes the role of the explanation offered in
paragraph 2?
A. Paragraph 2 questions this explanation by providing counterexamples of some
trees.
B. Paragraph 2 presents additional evidence supporting this explanation.
C. Paragraph 2 discusses some additional reasons why trees shed branches
D. Paragraph 2 points out some additional consequences for trees besides the
shedding of branches

5. The word “exposed” in the passage is closet in meaning to

A. distant
B. unprotected
C. easily replaced
D. unproductive

6. According to paragraph 2, what is true of the creosote bush of United States

deserts?
A. It tends to grow small branches during dry parts of the year.
B. It loses more water through its bark than through its leaves.
C. It loses its lower branches only after losing upper ones.
D. It sheds branches for the purpose of propagating itself.

Paragraph 3
How are branches shed? In the simplest cases, dead branches rot and fall off, or
healthy branches are snapped off by wind, snow, and animals. Some willows have a
brittle zone at the base of small branches that encourages breaking in the wind,
seemingly for propagation. Other cases of “natural pruning” are more startling: elm
trees, and to a certain extent others, such as oaks, have a reputation for dropping large
branches (up to half a meter in diameter) with no warning on calm, hot afternoons.
Such dramatic shedding appears to be due to a combination of internal water stress
coupled with heat expansion affecting cracks and decayed wood.

7. The phrase “with no warning” in the passage is closet in meaning to

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A. without any benefit
B. without any stress
C. without any indication beforehand
D. without any damage

8. All of the following are mentioned in paragraph 3 as a way in which branches can
be lost EXCEPT:
A. being broken off by the wind
B. being shed for propagation
C. becoming rotten
D. becoming too large in diameter

9. Which of the following is mentioned in paragraph 3 in the shedding of large

branches by oaks on calm, hot afternoons?
A. The development of a brittle zone at the base of the branches
B. The enlargement of cracks in the branches due to heat
C. The rise of sudden bursts of wind that snap off decayed wood
D. The seasonal need to propagate new trees

Paragraph 4
Many trees, however, shed branches deliberately. In this situation, branches are shed
in the same way as foliage in autumn by the prior formation of a corky layer that
leaves the wound sealed over with cork, which in turn is undergrown with wood the
following year. In hardwoods, branches up to a meter in length and several
centimeters in diameter can be shed normally after the leaves have fallen in the
autumn (maples are unusual in casting branches mainly in spring and early summer).
Oaks tend to shed small twigs up to the thickness of a pencil, beech may shed larger
ones, and birches dump whole branches of dead twigs. Pine trees shed their clusters of
needles (which really are short branches), and members of the redwood family shed
their small branch lets with leaves. Typically, in hardwood trees, something around 10
percent of terminal branches are lost each year through a mixture of deliberate
shedding and being broken off.

10. According to paragraph 4, what information can be learned from the deliberate
shedding of branches by the trees?
A. Limiting the size of branches being shed to comparatively small ones
B. Forming a new layer of wood to seal the wounded area immediately after shedding
C. Shedding leaves at the same time that branches are being shed
D. Forming a layer of protective tissue before branch shedding begins

Paragraph 5
Another way of reducing potential congestion is to make some branches smaller than
others. Branches in the shade grow smaller than those in the sun. But trees can also
regulate branch length from within. In many trees there is a clear distinction between
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long and short branches or shoots. The long shoots build the framework of the tree,
making it bigger. The job of the short shoots (called spur shoots by horticulturalists) is
to produce leaves, and commonly flowers, at more or less the same position every
year. To maintain flexibility, any one shoot can switch from long to short or vice versa
depending on internal factors, light levels, and damage.

11. The word “congestion” in the passage is closet in meaning to

A. loss
B. damage
C. overcrowding
D. stress

12. According to paragraph 5, what is the main purpose of the long branches or
shoots?
A. To regulate the length of large branches
B. To increase the size of the tree
C. To produce leaves and flowers
D. To help create shaded areas

13. Look at the four squares [ ] that indicate where the following sentence can be
added to the passage.
A tree will also shed branches if its water supply is insufficient.
Where would the sentence best fit? Click on a square [ ] to add the sentence to the
passage.

Paragraphs 1-2
One way trees prevent themselves from having too many branches is simply by
shedding (dropping off) branches once they have fulfilled their purpose. This happens
as the tree gets bigger and grows new outer layers of foliage that shade the inner and
lower branches. In most large trees, the center of the canopy contains only large
branches, small branches and fine twigs are found only at the canopy’s edge. In the
shaded center, the small branches that would once have occupied that space are long
gone. Trees like the true cypresses regularly shed small twigs complete with leaves
toward the end of summer. Most other trees shed only branches that prove
unproductive. If a branch is not producing enough carbohydrate to cover its own
running costs—i.e., it needs to be subsidized by other branches because, for example,
it is being shaded and receives little light—it will usually be got rid of. This prevents
unproductive branches from being a drain on the tree and removes the wind drag (the
force of air resistance) from useless branches. [A]

Branches are shed for reasons other than lack of light. [B] In dry parts of the world, it
is common for trees and shrubs to lose smaller branches to save water. [C] Small
branches have the thinnest bark (the protective outer covering of a tree) and greatest
surface area and thus are the source of most water loss once the leaves have been lost.
364
[D] The creosote bush of United States deserts self-prunes, or removes parts of itself,
in the face of extreme heat or drought, starting from the highest and most exposed
twigs and working downward to bigger and bigger branches, it’s a desperate act
because if the creosote bush loses too much food, it dies. Shedding branches can also
be useful for self-propagation. Most poplar trees and willow trees characteristic of
waterways will readily drop branches, which take root when washed up on muddy
banks further downstream.

14. Directions: An introductory sentence for a brief summary of the passage is

provided below. Complete the summary by selecting the THREE answer choices that
express the most important ideas in the passage. Some answer choices do not belong
in the summary because they express ideas that are not presented in the passage or are
minor ideas in the passage. This question is worth 2 points.
Drag your choices to the spaces where they belong. To review the passage, click on
View Text.

For trees to remain healthy as they grow and as circumstances change, tree branches
must change in various ways.
Answer Choices

A. Trees can benefit from shedding inefficient branches that consume more
carbohydrates than they produce or that are a major source of water loss.
B. Branches can be lost as a result of damage from whether, animals, or disease, but
they can also be shed when they are no longer useful, much as leaves are shed in
autumn.
C. While branch shedding is common and may be necessary for a tree’s survival, the
corky layer that forms at sites where branches have been shed prevents additional
growth in those areas for several years.
D. Shedding large branches is such a desperate act for survival that the creosote bush
is one of the few plants to use this mechanism for removing wood.
E. Larger trees can self-propagate when water stress and heat expansion break off
branches, as long as the shed branches fall on or can be transported to a location
favorable for taking root.
F. Trees prevent branch overcrowding in part by varying branch length through
internal mechanisms such as having shoots that can switch from long to short or from
short to long, as needed.

Early life-forms and Earth’s Atmosphere(2014-06-15 考过一次)

Paragraph 1
Position relative to the Sun. Second, once life began on Earth, simple early life-forms
(photosynthetic bacteria) slowly but inexorably altered the environment in a manner
that not only maintained life but also paved the way for later, complex life-forms.
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These changes allowed later organisms to evolve and thrive. Humans and other higher
organisms owe their life-supporting environment to these early life-forms.

1. The word “altered” in the passage is closet in meaning to

 transformed
 protected
 made use of
 adapted to

2. Paragraph 1 supports which of the following inferences?

 After complex life forms arose on Earth, bacteria quickly evolved in order to
maintain favorable conditions for life.
 Early life forms on Earth arose from the process of photosynthesis.
 The development of complex life on Earth depended on the presence of bacteria
that could be consumed by larger organisms.
 Complex life forms on Earth may not have evolved if Earth had been farther from
or closer to the Sun.

Paragraph 2
Earth’s earliest atmosphere contained several gases: hydrogen, water vapor, ammonia,
nitrogen, methane, and carbon dioxide, but no oxygen. Gas mixtures emitted from
present-day volcanoes resemble this early atmosphere, suggesting its origin from
volcanic eruptions. In Earth’s earliest atmosphere, methane and carbon dioxide
occurred at much higher levels than at present—a circumstance that was favorable for
early life. Methane and carbon dioxide are greenhouse gases that warm atmospheres
by retarding loss of heat to space. These two gases kept Earth warm during the Sun’s
early history, when the Sun did not burn as brightly as it now does. (An early dim
period, with later brightening, is normal for stars of our Sun’s type.)

3. The word “emitted” in the passage is closet in meaning to

 disappearing
 examined
 released
 taken

4. The word “retarding” in the passage is closet in meaning to

 regulating
 slowing
 restoring
 directing

5. In paragraph 2, why does the author provide the information that methane and
carbon dioxide kept the Earth warm during the Sun’s early history?
 To explain how the early Earth and the early Sun were related
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 To support the claim that methane and carbon dioxide are greenhouse gases
 To explain why the high levels of methane and carbon dioxide in Earth’s early
atmosphere were favorable for early life
 To suggest that these gases affect how brightly the Sun burns

6. Paragraph 2 supports which of the following statements about methane and carbon
dioxide present in Earth’s earliest atmosphere?
 They slowed down the loss of heat from Earth’s atmosphere.
 They caused the sunlight to be less bright than it currently is.
 They occurred in smaller amounts than they currently do.
 They prevented the development of early life-forms.

Paragraph 3
Earth’s modern atmosphere, which is 78 percent nitrogen gas, 21 percent oxygen, and
about 1 percent argon, water vapor, ozone, and carbon dioxide, differs dramatically
from the earliest atmosphere just described. The modern atmosphere supports many
forms of complex life that would not have been able to exist in Earth’s first
atmosphere because the oxygen level was too low. Also, if atmospheric methane and
carbon dioxide were as abundant now as they were in Earth’s earliest atmosphere, the
planet’s temperature would likely be too hot for most species living today. How and
when did the atmosphere change?

7. The word “abundant” in the passage is closet in meaning to

 pure
 balanced
 plentiful
 warm

8. According to paragraph 2 and 3, which of the following is one way in which

Earth’s early atmosphere differed from its current atmosphere?
 It had fewer greenhouse gases.
 It was warmer.
 It had lower levels of carbon dioxide.
 It did not contain methane.

Paragraph 4
The answer to this riddle lies in the metabolic activity of early photosynthetic
life-forms that slowly but surely transformed the chemical composition of Earth’s
atmosphere. Some of these early organisms were photosynthetic relatives of modern
cyanobacteria (blue-green bacteria). In the process of photosynthesis, carbon dioxide
gas combined with water yields oxygen. In Earth’s early days, all over the planet
countless photosynthetic bacteria performed photosynthesis. Together, these ancient
bacteria removed massive amounts of carbon dioxide from Earth’s atmosphere by
converting it to solid organic carbon. These ancient bacteria also released huge
367
quantities of oxygen into the atmosphere. Other ancient bacteria consumed methane,
greatly reducing its amount in the atmosphere. When our Sun later became hotter, the
continued removal of atmospheric carbon dioxide and methane by early bacteria kept
Earth’s climate from becoming too hot to sustain life. Modern cyanobacteria still
provide these valuable services today.

9. The word “sustain” in the passage is closet in meaning to

 change
 generate
 destroy
 support

10. According to paragraph 4, ancient bacteria changed the chemical composition of

Earth’s atmosphere by performing all of the following activities EXCEPT
 raising the temperature of the atmosphere
 removing methane and carbon dioxide
 creating organic carbon
 producing oxygen

Paragraph 5
The bacterial oxygen release improved conditions for life in two ways. First, oxygen
is essential for the metabolic process known as cell respiration that allows cells to
efficiently harvest energy from organic food. Second, oxygen in the upper atmosphere
reacts to form a protective shield of ozone. Earth is constantly bombarded by harmful
ultraviolet (UV) radiation from the Sun. Today, Earth’s upper-atmosphere ozone
shield absorbs enough UV to allow diverse forms of life to survive. But because early
Earth lacked oxygen in its atmosphere, it also lacked a protective ozone barrier. As a
result, early life on Earth was confined to the oceans, where the water absorbed the
UV radiation. Only after oxygen released by ancient bacteria drifted up into the upper
atmosphere and reacted with other oxygen molecules to form a protective layer of
ozone, could life flourish at the surface and on the land. 【The absence of an oxygen
atmosphere on Mars and other planets in our solar system means that these planets
also lack an ozone shield that would protect surface-dwelling life from UV radiation. 】
The surface of Mars is bombarded with deadly radiation; if any life exists on Mars, it
would almost certainly be subterranean.

11. It can be inferred from paragraph 5 that early life-forms on Earth were confined to
the oceans because
 the thick ozone layer at the time would have made it difficult for them to survive
on land
 water was the only available protection they had against ultraviolet radiation
 land provided them with only limited amounts of water needed for survival
 their metabolic systems were inefficient
Paragraph 5 is marked with an arrow [→]
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12. Which of the sentences below best expresses the essential information in the
highlighted sentence in the passage? Incorrect choices change the meaning in
important ways or leave out essential information.
 Any life forms that may have existed on other planets probably were destroyed by
UV radiation.
 Other planets in our solar system lack the oxygen atmosphere that helps explain
why life exists on Earth.
 The absence of oxygen on other planets means that those planets lack an ozone
shield to protect life forms against UV radiation.
 Life forms cannot survive UV radiation without the protection of an ozone shield.

13. Look at the four squares [■] that indicate where the following sentence can be
added to the passage.
But protection against what?
Where would the sentence best fit? Click on a square [■] to add the sentence to the
passage.

Paragraph 5
The bacterial oxygen release improved conditions for life in two ways. First, oxygen
is essential for the metabolic process known as cell respiration that allows cells to
efficiently harvest energy from organic food. Second, oxygen in the upper atmosphere
reacts to form a protective shield of ozone. ■Earth is constantly bombarded by
harmful ultraviolet (UV radiation from the Sun. ■Today, Earth’s upper-atmosphere
ozone shield absorbs enough UV to allow diverse forms of life to survive. ■But
because early Earth lacked oxygen in its atmosphere, it also lacked a protective ozone
barrier. ■As a result, early life on Earth was confined to the oceans, where the water
absorbed the UV radiation. Only after oxygen released by ancient bacteria drifted up
into the upper atmosphere and reacted with other oxygen molecules to form a
protective layer of ozone, could life flourish at the surface and on the land. The
absence of an oxygen atmosphere on Mars and other planets in our solar system
means that these planets also lack an ozone shield that would protect surface-dwelling
life from UV radiation. The surface of Mars is bombarded with deadly radiation; if
any life exists on Mars, it would almost certainly be subterranean.

14. Directions: An introductory sentence for a brief summary of the passage is

provided below. Complete the summary by selecting the THREE answer choices that
express the most important ideas in the passage. Some answer choices do not belong
in the summary because they express ideas that are not presented in the passage or are
minor ideas in the passage. This question is worth 2 points.
Earth’s earliest atmosphere was transformed in ways that allowed the development of
complex life forms.

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A. Volcanoes changed Earth’s earliest atmosphere in ways that allowed life to develop,
and bacteria that used oxygen produced by photosynthesis further altered the
atmosphere to what we find today.
B. When the sun became brighter, early bacteria removed methane and carbon dioxide
from the atmosphere, preventing Earth from becoming too hot for life to survive.
C. Early bacteria provided the oxygen that was needed to support the metabolism of
complex life forms and to form an ozone shield against deadly UV radiation.
D. Volcanic carbon dioxide in Earth’s early atmosphere kept Earth warm enough for
life to begin during the time when the Sun was too dim to provide much warmth.
E. Earth has been able to support life because its position relative to the Sun provided
it with enough heat, but not too much heat for early bacteria to evolve.
F. Complex life evolved on the Earth’s surface, but not on Mars or other planets in the
solar system because on those planets, early surface life was killed by UV radiation.

The Origins of Plant and Animal Domestication

The Origins of Plant and Animal Domestication 答案：DCCBB CCABD DB ABF

Preventing Overgrowth among Tree Branches

Preventing Overgrowth among Tree Branches 答案：BADCB CCDBD CBB ABF

第三篇 Early life-forms and Earth’s Atmosphere 答案：

ADCBC, ACBDA, BCA, 234
此篇暂无解析

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