The earth（地球）is our home．We must take care of it．①This means keeping the land，air and water clean．
Pollution（污染）is a“dirty”（脏）word．To pollute means to make（使）things dirty．Pollution comes in many ways．We see it，smell it and drink it．②Pollution is beginning to do harm（伤害）to our health，and even（甚至）to our life．
Man has been polluting（人类一直在污染）the earth from the time he first made fire（生火），washed his clothes in the river and threw his rubbish（垃圾）on the ground．③Many years ago，the problem was not so serious（严重）because there were not so many people．All dirty things would soon be covered（覆盖）up．There was a lot of clean air，land and water．④When the land was used up（用完）or the river was dirty in a place，people moved to another place．But this is no longer true．Man is now slowly polluting the whole（整个）world．⑤We are glad that a lot of people are working hard to get rid of（清除）pollution now．
参考答案：1．这就意味着要保持土地、空气和水的清洁。
2．污染正开始危害我们的健康，甚至危及生命。
3．许多年以前这一问题还不太严重，因为人不太多。
4．当一个地方的土地开发完毕或河流变脏时，人们就搬到另一个地方去了。
5．我们感到高兴的是现在有许多人正在为清除污染而努力工作着。
