The Earth is 1. _______ (we) home. And we must take good 2. _______ (careful) of it. That is to say We must keep the land, air 3. _______water clean. Many years ago, pollution 4. _______ (be) not so serious, because the population of the Earth was not so large as today. There was enough fresh air, good agricultural land and clean water. When the land or the river was dirty and 5. _______ (pollute) in one place, men left there and moved to another place. People are polluting 6. _______ whole world now. In some aspects, it seems that the more people there are in one place, the 7. _______ (bad) environment they may live in. Perhaps you are worried that it is endless 8. _______ people to produce pollution. 9. _______ (Lucky), more and more people have come to know the danger of pollution. And we can find more and more people are 10. _______ (work) hard to protect our Earth.