阅读下面短文，从短文后的选项中选出可以填入空白处的最佳选项。选项中有两项为多余选项。
The earth is our home. We must take care of it. This means keeping the land，air and water clean.
Pollution is a “dirty word”. To pollute means to make things unfit(不合适的) or unclean to use. 16 We see it，smell it，taste it and drink it. Pollution is beginning to threaten(威胁) our health，our happiness and our life.
Humans have been polluting the earth since they first built fires，washed clothes in the river and threw waste on the ground. 17 At first the problem was not so serious because there was plenty of clean air，land and water. 18 All the dirty things could be naturally absorbed(吸收) and broken down. But this is no longer true. The increase of the population and the development of industry have changed that. Humans are slowly polluting the environment.
Through the use of chemicals，people have polluted the land and killed the animals. By pouring waste water and chemicals into rivers and lakes，we have polluted our drinking water，killing the fish. 19 More people，more waste.
Where will this all end? Are we turning the world into a big rubbish dump，or is there any hope that we can get rid of pollution? 20 A large number of people are now working hard to bring pollution under control.
A. There weren’t so many people then and their needs were fewer.
B. Pollution comes in many ways.
C. Our increasing population is part of the problem.
D. Man couldn’t probably live on the earth.
E. When the land was worn out or the water became too dirty，people would move to another place.
F. Luckily，millions of people have been warned of the danger of pollution.
G. Many factories have stopped production to reduce air pollution.
16. 17. 18.
19. 20.