Pollution happens when the environment is dirtied, by waste, chemicals and other harmful substances. Pollution is a problem all over the world. But it is especially bad in large cities with a lot of industries and cars. 1　

Wildfires, volcanoes, and industrial chemicals cause some air pollution. But most air pollution comes from burning fossil fuels. These include coal, oil, and natural gas. The burning of fossil fuels may release harmful gases. Air pollution may cause such diseases as cancer and asthma. It also leads to polluted rain that can harm living things. 2　 Finally, air pollution damages the ozone layer (臭氧层), which is important because it protects Earth against harmful rays from the sun.

Causes of water pollution are easy to see. People dump rubbish and dirty water into rivers, lakes and oceans. Factories or cities sometimes release poisonous chemicals, and other wastes into water. These chemicals may make the groundwater unfit to drink. 3　

Littering, or throwing garbage on the ground, is a form of land pollution. Litter can destroy the habits of plants and animals. The buildup of dangerous chemicals in the ground is another form of land pollution. The chemicals may come from farms or factories. 4　 They may even harm people who eat the polluted plants and animals.

Many governments, environmental groups, and ordinary people are working to control pollution. Governments have passed laws to keep people from releasing dangerous chemicals into the environment. 5　 Instead they are getting power from the sun, wind, water, and other energy sources that produce less pollution. Many communities use recycling to reduce pollution.

A. Farmers use chemicals to help crops grow.

B. This type of pollution may be seen in big cities.

C. They also can harm fish and other forms of life.

D. These chemicals can spread to plants and animals.

E. In addition, air pollution may be a cause of global warming.

F. These are three main forms of pollution: air, water and land.

G. Some companies and people are trying to use fewer fossil fuels.

【文章大意】短文主要介绍了污染的三种主要形式和控制污染的措施。

1. 【解析】选F。由第二到四段对air pollution, water pollution和land pollution的介绍可知, 空白处的意思是"污染的三种主要形式: 空气污染, 水污染和土地污染。"因此答案选F。

2. 【解析】选E。由该空前面的"Air pollution may cause such diseases"和"It also leads to polluted rain"以及后面的"Finally, air pollution damages the ozone layer"可知, 空白处讲的也是大气污染的影响, E项内容"此外, 空气污染也可能是全球变暖的原因", 符合此处语境。

3. 【解析】选C。本段主要讲述水污染的原因及影响, 由该空前面的"These chemicals may make the groundwater unfit to drink. "可知, C项内容"这些化学物质还会危害鱼类和其他生物"符合语境。

4. 【解析】选D。根据该空前面对污染土地的化学物质的描述以及空白后面"They may even harm people who eat the polluted plants and animals. "一句所提供的信息可知, 这些化学物质会蔓延到植物和动物身上, 甚至会危害人类。故D项为正确答案。