PASSAGE 13

A Thirsty World来源：考试大

　　The world is not only hungry， it is also thirsty for water. This may seem strange to you， since nearly 75% of the earth's surface is covered with water. But about 97% of this huge amount is sea-water， or salt water. Man can only drink and use the other 3% ——the fresh water that comes from rivers， lakes， underground， and other sources. ____1____， because some of it is in the form of icebergs and glaciers. Even worse， some of it has been polluted.来源：考试大

　　In addition to stopping wasting our precious water， one more useful step we should take is to develop ways of reusing it. ____3____， but only on a small scale.
　　Today， in most large cities， water is used only once and it eventually returns to the sea or runs into underground storage tanks. ____4____ that has been used to a purifying plant. There it can be filtered and treated with chemicals so that it can be used again just as if it were fresh from a spring.
　　___5____， we still would not have enough. Where could we turn next？ To the oceans！ All we'd have to do to make use of the vast amount of sea-water is -remove the salt. This salt-removing process is already in use in many parts of the world.
　　So if we take all these steps， we'll be in no danger of drying up！

　　A. A limited water supply来源：考试大
　　B. But it is possible to pipe water
　　C. It is possible to purify large amounts of sea water
　　D. But even if every large city purified and reused its water
　　E. And we cannot even use all of tha
　　F. Experiments have already been done in this field

　　KEYS： EAFBD