根据材料内容，选择正确答案。
The earth is about 4,600 million years old. Modern man has lived on the earth for only 35,000 years, but during that time, we have changed our planet in many ways. Many of the things that we have done are good, but more are not good for the earth.
Water pollution
A lot of people, birds and fish die each day because of water pollution. Factories have polluted the land and the water. As a result, many river and lakes are now dead.
Air pollution
In big cities, factories, as well as cars, trucks and buses are the biggest cause of air pollution. Many people in cities now have bad health problems. For example, Mexico city used to be a beautiful sunny capital, but today it is almost covered by thick brown clouds.
Soil pollution
In order to have a good harvest, most of the farmers use chemicals too much on their fields. That's bad for the soil. But this kind of pollution is difficult to stop.
Hope for the future
These problems are very serious for our future, so all of us should do something to improve our environment. If we can stop pollution, our planet will become more and more beautiful and our health will be better. Let's be greener people.
____ are different from ours.
