Read the paragraph and answer the questions in the chatbox.

Do it in a group. One group consists of 3 participants.

Identifying the Topic of a Paragraph

EXERCISE 1

A. Read each paragraph and underline words that are repeated. Then write a topic that is not
too specific or too general.

Mexico City: Water Shortages and a Sinking City

1. Like many other fast-growing cities around the world, Mexico City is facing
severe water shortages. Many of its 20 million inhabitants receive only one hour of
piped water per week. Others receive none at all for weeks on end. Those who can afford
the expense build their own home water system to catch and keep rainwater to
supplement the city water. The situation, according to international experts, is the result
of a combination of factors. First, the system of pipes is old and poorly managed, with the
result that the pipes lose almost 40 percent of the water that they distribute around
the city. Second, the demand for water, which has grown with the rapid population
growth, far exceeds the supply. Furthermore, the water is consumed not only by residents
for household use, but also by thirsty industries such as beer-brewers and soft-drink
bottlers, and there is little incentive' for them to conserve or recycle water.2

incentive: something that encourages you to do something

conserve: to use less
Topic: severe water shortage in city/ in Mexico City

2. The current water shortages in Mexico City contrast remarkably with the city's situation
in the past. When the Spanish arrived at the Aztec capital in 1519, they found stone
buildings and gardens set on an island in the middle of a vast series of interconnected
lakes—an "enchanted vision," according to one Spanish soldier. The Spanish destroyed
the buildings, and began draining' the water from the lakes to build what became Mexico
City. For the next four centuries, the city was able to meet its water needs from springs,
shallow wells, and the remaining lake water. In the mid-nineteenth century, the residents
of the city began taking water from the underlying aquifer. In the twentieth century, as
2

water needs grew and supplies from the aquifer became inadequate, city authorities
brought water up from two nearby river systems. Twenty-five years ago, they began
piping in water from 80 miles (130 km) away. Because Mexico City is located on a
highland, the water must all be pumped uphill at considerable expense.
drain: to make the water flow away
2 aquifer: a layer of stone or earth under the surface of the ground that contains water

Topic: current water shortages in Mexico City contrast with the past

B. Compare your answers with those of another student. If you disagree, explain your answers and
look back at the paragraphs to check your work.

Topic Sentences
Paragraphs in English usually contain a topic sentence that lets the reader know what the
paragraph is about. Although this sentence is usually near the beginning of the paragraph, it can
also be found in the middle or at the end.

EXERCISE 2
A. Each of the paragraphs is missing a topic sentence. The missing sentences are listed at the end of
the exercise (with one extra sentence). Working with another student, read the paragraphs and write
the letter of the sentence that fits each paragraph best.
The Pollution of the Oceans

1. No one can calculate the quantity of solid waste that has been dumped' in the world's
oceans, but the total certainly exceeds many millions of tons. For example, from 1880 to
1895, 75 percent of the solid waste from New York City was dumped untreated into the
Atlantic Ocean. Although it is now prohibited by law, the dumping of solid waste,
including wastewater sludge, industrial waste, and high-level radioactive waste were
2

common in the United States until 1970. Cruise ships and huge floating fishing factories
still regularly dispose of their solid waste products directly into the ocean.
Topic Sentence : The oceans have long served as a vast dumping ground for all kinds of
waste

1 dump: to get rid of something you do not want

sludge: mud, waste, and oil mixed together
2. The earth naturally recycles water and refreshes the land in what is called the
hydrological cycle. The hydrological cycle not only renews the supply of water, but
cleans it as well. The process begins as heat from the sun causes sea water, 97 percent of
the earth's total water reserve, to evaporate' and form clouds. Because water evaporates at
lower temperatures than most pollutants, the water vapor that rises from the seas is
relatively pure and free of the contaminants, which are left behind. Next, water returns to
earth as rain, which drains into streams and rivers and rushes toward the sea.
Topic Sentence : Although the hydrological cycle produces clean water in the form of
rain, it does not remove the pollutants that steadily build up in the oceans.

3. Chemicals, petroleum products, and other dangerous substances such as radioactive

materials remain in the ocean, polluting it permanently. The polluted ocean water kills
fish or makes them dangerous to eat, posing health problems for those who consume
them. It kills the tiny sea creatures that are the source of food for larger fish, sharks, and
whales. It also spoils a source of great beauty and pleasure when some solid waste is
thrown onto beaches during storms. Discharged petroleum products are frequently found
on beaches and they not only ruin the beach, the petroleum residue' kills hundreds of
shore birds.
Topic Sentence : These are just a few of the problems caused by using the oceans as
dumping grounds.

4. Nonpoint pollutants are dumped into lakes, rivers, and streams that may be far away from
any ocean. However, these pollutants flow, eventually, into the oceans. They can come
from a variety of sources, from road salt to agricultural pesticides. One source of
 nonpoint pollution is runoff from farming, including fertilizers, manure, and pesticides.
Another source is industrial runoff, including heavy metals, phosphorous, and many other
chemicals. Urban runoff (oils, salts, various chemicals) and atmospheric fallout of
airborne pollution are other sources of nonpoint pollutants that reach the oceans.
Topic Sentence : Some pollutants in the ocean are not dumped there directly.

5. This includes water and waste from sinks, toilets, washing machines, and bathtubs. The
problem with this type of waste is that it provides massive amounts of nutrients for water
plants, such as algae, so that they grow rapidly. This sudden growth causes
concentrations or algae blooms, which use up the oxygen in the water. As the oxygen
levels of the water decline, many organisms suffer and die, and the ocean ecosystem is
radically altered. This can be prevented by the installation of waste treatment plants that
prevent waste from entering the sea, but such facilities do not exist in many poorer
countries.
Topic Sentence : Some pollutants in the ocean are not dumped there directly.

evaporate: when a liquid changes into a gas

4 discharged: to send out from someplace

5 residue: something left after most of the material is gone

Missing topic sentences:

a. Although the hydrological cycle produces clean water in the form of rain, it does not
remove the pollutants that steadily build up in the oceans.
b. New laws and regulations make it difficult for people to dump their trash into the oceans.
c. The oceans have long served as a vast dumping ground for all kinds of waste.
d. These are just a few of the problems caused by using the oceans as dumping grounds.
e. Wastewater dumping is yet another major form of ocean pollution.
f. Some pollutants in the ocean are not dumped there directly.

A. Compare your answers with those of another pair of students. If you disagree, explain your
answers and look back at the paragraphs to check your work.

Main Ideas of Paragraphs

Topic sentences and main ideas
In addition to stating the topic, most topic sentences also tell the writer's main idea, or in other
words, the idea that the writer wants to express about the topic. To explain the idea, the writer
includes several supporting details in the paragraph and these details are more
specific than the main idea.
Inferring the Main Idea
In some paragraphs, the topic sentence may not state the complete main idea. The topic may be
stated in one sentence, and the writer's idea about the topic may be expressed in another sentence
or in several sentences in the paragraph. In this case, the reader must combine ideas from several
sentences to infer the complete main idea.

Note: To make sure that it is really expressing a complete idea, the main idea statement should
always be stated in a complete sentence with a subject and verb.

EXERCISE 3

A. Working with another student, read the paragraph, write the topic, and underline the supporting
facts and ideas. Then choose the best main idea statement.

Floodplains are the flat land near a river that is covered with water when the river rises following
a storm. They provide several benefits. They can control flooding when the waters of a narrow
river rise rapidly. As soon as the river's water has exceeded its banks and enters a floodplain, the
water spreads out over a wide area and slows down. There, the floodplain holds the water,
allowing it to be slowly released into the river system and into underground bodies of water.
Floodplains also help clean rivers and streams. They keep the water long enough for sediment
(small particles of dust, rock, and organic matter) to settle into the earth under the floodplain.
This keeps the sediment
out of the river or stream.
Topic: Flood, river, water
Main idea:
a. Floodplains are the flat land near a river that is covered with water when the river
rises following a storm.
b. Floodplains can control flooding when the waters of a narrow river rise rapidly.
c. Floodplains near a river provide several benefits.

A. Compare your answers with those of another pair of students. If you disagree, explain your answers.
Discuss the other main idea choices and explain why they were too general or too specific.

EXERCISE 4

A. Working with another student, read each paragraph, write the topic, and underline the supporting
facts and ideas. Then choose the best main idea statement.

Controlling Water in the Netherlands

The Netherlands, in Europe,
Identifying the Topic of a Paragraph
EXERCISE 1

A. Read each paragraph and underline words that are repeated. Then write a topic that is not
too specific or too general.

Mexico City: Water Shortages and a Sinking City

 1. Like many other fast-growing cities around the world, Mexico City is facing
severe water shortages. Many of its 20 million inhabitants receive only one hour of
piped water per week. Others receive none at all for weeks on end. Those who can afford
the expense build their own home water system to catch and keep rainwater to
supplement the city water. The situation, according to international experts, is the result
of a combination of factors. First, the system of pipes is old and poorly managed, with the
result that the pipes lose almost 40 percent of the water that they distribute around
the city. Second, the demand for water, which has grown with the rapid population
growth, far exceeds the supply. Furthermore, the water is consumed not only by residents
for household use, but also by thirsty industries such as beer-brewers and soft-drink
bottlers, and there is little incentive' for them to conserve or recycle water.
2

incentive: something that encourages you to do something

conserve: to use less
Topic: severe water shortage in city/ in Mexico City

2. The current water shortages in Mexico City contrast remarkably with the city's situation
in the past. When the Spanish arrived at the Aztec capital in 1519, they found stone
buildings and gardens set on an island in the middle of a vast series of interconnected
lakes—an "enchanted vision," according to one Spanish soldier. The Spanish destroyed
the buildings, and began draining' the water from the lakes to build what became Mexico
City. For the next four centuries, the city was able to meet its water needs from springs,
shallow wells, and the remaining lake water. In the mid-nineteenth century, the residents
of the city began taking water from the underlying aquifer. In the twentieth century, as
2

water needs grew and supplies from the aquifer became inadequate, city authorities
brought water up from two nearby river systems. Twenty-five years ago, they began
piping in water from 80 miles (130 km) away. Because Mexico City is located on a
highland, the water must all be pumped uphill at considerable expense.
drain: to make the water flow away
2 aquifer: a layer of stone or earth under the surface of the ground that contains water

Topic: current water shortages in Mexico City contrast with the past

B. Compare your answers with those of another student. If you disagree, explain your answers and
look back at the paragraphs to check your work.

Topic Sentences
Paragraphs in English usually contain a topic sentence that lets the reader know what the
paragraph is about. Although this sentence is usually near the beginning of the paragraph, it can
also be found in the middle or at the end.

EXERCISE 2
A. Each of the paragraphs is missing a topic sentence. The missing sentences are listed at the end of
the exercise (with one extra sentence). Working with another student, read the paragraphs and write
the letter of the sentence that fits each paragraph best.
The Pollution of the Oceans

1. No one can calculate the quantity of solid waste that has been dumped' in the world's
oceans, but the total certainly exceeds many millions of tons. For example, from 1880 to
1895, 75 percent of the solid waste from New York City was dumped untreated into the
 Atlantic Ocean. Although it is now prohibited by law, the dumping of solid waste,
including wastewater sludge, industrial waste, and high-level radioactive waste were
2

common in the United States until 1970. Cruise ships and huge floating fishing factories
still regularly dispose of their solid waste products directly into the ocean.
Topic Sentence : The oceans have long served as a vast dumping ground for all kinds of
waste

1 dump: to get rid of something you do not want

2 sludge: mud, waste, and oil mixed together
2. The earth naturally recycles water and refreshes the land in what is called the
hydrological cycle. The hydrological cycle not only renews the supply of water, but
cleans it as well. The process begins as heat from the sun causes sea water, 97 percent of
the earth's total water reserve, to evaporate' and form clouds. Because water evaporates at
lower temperatures than most pollutants, the water vapor that rises from the seas is
relatively pure and free of the contaminants, which are left behind. Next, water returns to
earth as rain, which drains into streams and rivers and rushes toward the sea.
Topic Sentence : Although the hydrological cycle produces clean water in the form of
rain, it does not remove the pollutants that steadily build up in the oceans.

3. Chemicals, petroleum products, and other dangerous substances such as radioactive

materials remain in the ocean, polluting it permanently. The polluted ocean water kills
fish or makes them dangerous to eat, posing health problems for those who consume
them. It kills the tiny sea creatures that are the source of food for larger fish, sharks, and
whales. It also spoils a source of great beauty and pleasure when some solid waste is
thrown onto beaches during storms. Discharged petroleum products are frequently found
on beaches and they not only ruin the beach, the petroleum residue' kills hundreds of
shore birds.
Topic Sentence : These are just a few of the problems caused by using the oceans as
dumping grounds.

4. Nonpoint pollutants are dumped into lakes, rivers, and streams that may be far away from
any ocean. However, these pollutants flow, eventually, into the oceans. They can come
from a variety of sources, from road salt to agricultural pesticides. One source of
nonpoint pollution is runoff from farming, including fertilizers, manure, and pesticides.
Another source is industrial runoff, including heavy metals, phosphorous, and many other
chemicals. Urban runoff (oils, salts, various chemicals) and atmospheric fallout of
airborne pollution are other sources of nonpoint pollutants that reach the oceans.
Topic Sentence : Some pollutants in the ocean are not dumped there directly.

5. This includes water and waste from sinks, toilets, washing machines, and bathtubs. The
problem with this type of waste is that it provides massive amounts of nutrients for water
 plants, such as algae, so that they grow rapidly. This sudden growth causes
concentrations or algae blooms, which use up the oxygen in the water. As the oxygen
levels of the water decline, many organisms suffer and die, and the ocean ecosystem is
radically altered. This can be prevented by the installation of waste treatment plants that
prevent waste from entering the sea, but such facilities do not exist in many poorer
countries.
Topic Sentence : Some pollutants in the ocean are not dumped there directly.

evaporate: when a liquid changes into a gas

4 discharged: to send out from someplace

5 residue: something left after most of the material is gone

Missing topic sentences:

a. Although the hydrological cycle produces clean water in the form of rain, it does not
remove the pollutants that steadily build up in the oceans.
b. New laws and regulations make it difficult for people to dump their trash into the oceans.
c. The oceans have long served as a vast dumping ground for all kinds of waste.
d. These are just a few of the problems caused by using the oceans as dumping grounds.
e. Wastewater dumping is yet another major form of ocean pollution.
f. Some pollutants in the ocean are not dumped there directly.

A. Compare your answers with those of another pair of students. If you disagree, explain your
answers and look back at the paragraphs to check your work.

Main Ideas of Paragraphs

Topic sentences and main ideas
In addition to stating the topic, most topic sentences also tell the writer's main idea, or in other
words, the idea that the writer wants to express about the topic. To explain the idea, the writer
includes several supporting details in the paragraph and these details are more
specific than the main idea.
Inferring the Main Idea
In some paragraphs, the topic sentence may not state the complete main idea. The topic may be
stated in one sentence, and the writer's idea about the topic may be expressed in another sentence
or in several sentences in the paragraph. In this case, the reader must combine ideas from several
sentences to infer the complete main idea.

Note: To make sure that it is really expressing a complete idea, the main idea statement should
always be stated in a complete sentence with a subject and verb.

EXERCISE 3
 A. Working with another student, read the paragraph, write the topic, and underline the supporting
facts and ideas. Then choose the best main idea statement.

Floodplains are the flat land near a river that is covered with water when the river rises following
a storm. They provide several benefits. They can control flooding when the waters of a narrow
river rise rapidly. As soon as the river's water has exceeded its banks and enters a floodplain, the
water spreads out over a wide area and slows down. There, the floodplain holds the water,
allowing it to be slowly released into the river system and into underground bodies of water.
Floodplains also help clean rivers and streams. They keep the water long enough for sediment
(small particles of dust, rock, and organic matter) to settle into the earth under the floodplain.
This keeps the sediment
out of the river or stream.
Topic: Flood, river, water
Main idea:
a. Floodplains are the flat land near a river that is covered with water when the river rises
following a storm.
b. Floodplains can control flooding when the waters of a narrow river rise rapidly.
c. Floodplains near a river provide several benefits.

A. Compare your answers with those of another pair of students. If you disagree, explain your answers.
Discuss the other main idea choices and explain why they were too general or too specific.

EXERCISE 4

A. Working with another student, read each paragraph, write the topic, and underline the supporting
facts and ideas. Then choose the best main idea statement.

Controlling Water in the Netherlands

The Netherlands, in Europe, is more than 60 percent near or below sea level. Flooding has
always been a major worry because its major cities, factories, and greenhouse farms are built on
floodplains. The greatest risk of flooding comes from the North Sea itself with its severe winter
storms and massive tides. However, flooding can also occur along the Rhine, Maas, and Scheldt
Rivers, which are swollen every spring with snowmelt from the Alps. And when these major
rivers meet the North Sea, they form a delta region that consists of additional floodplains.
Topic: Greatest risk of floodplain in the Netherland caused by the North Sea
Main idea:
a. The Netherlands, in Europe, is more than 60 percent near or below sea level.
b. Floods in the Netherlands are caused by severe winter storms.
c. The Netherlands is at a high risk of flooding because much of it is on floodplains.
is more than 60 percent near or below sea level. Flooding has always been a major worry
because its major cities, factories, and greenhouse farms are built on floodplains. The greatest
risk of flooding comes from the North Sea itself with its severe winter storms and massive tides.
However, flooding can also occur along the Rhine, Maas, and Scheldt Rivers, which are swollen
every spring with snowmelt from the Alps. And when these major rivers meet the North Sea,
they form a delta region that consists of additional floodplains.
Topic: Greatest risk of floodplain in the Netherland caused by the North Sea
Main idea:
a. The Netherlands, in Europe, is more than 60 percent near or below sea level.
b. Floods in the Netherlands are caused by severe winter storms.
c. The Netherlands is at a high risk of flooding because much of it is on floodplains.