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We are destroying the Earth. The sea and rivers are too (1) _________ to swim in. There is so much smoke in the (2) _________ that it is unhealthy to live in many of the world's cities. In one well-known city, for example, poisonous gases from cars (3) _________ the air so much that policemen have to wear oxygen mask. We have cut (4) _________ so many trees that there are now vast areas of wasteland all over the world. As a result, farmers in part of Africa cannot grow (5) _________ to eat. In certain countries in Asia there is so little rice. Moreover, we do not take enough care of the countryside. Wild animals are quickly disappearing. For instance , tigers are (6) _________ in India how because we have killed too many for them to survive. However, it isn't so simple to talk about the problem. We must act now before it is too late to do anything about it. Join us now. Save the Earth.
         1.         A. clean           B. cool               C. dirty              D. cold
         2.         A. air                B. river              C. lake              D. stream
         3.         A. pollute         B. run                C. breathe         D. grow
         4.         A. back             B. down            C. out                D. in
         5.         A. many           B. enough         C. then               D. that
         6.         A. rare              B. plenty           C. many             D. much