A. all af that B. as if it were C. fresh water supply D. in this field A. A limited【T13】______ B. so that it

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问题 A. all af that              B. as if it were
C. fresh water supply       D. in this field
A. A limited【T13】______
B. so that it can be used again just【T14】______ from a spring
C. And we cannot even use【T15】______
D. Experiments have already been done【T16】______
    The world is not only hungry, it is also thirsty for water. It seems there is plenty of water, but about 97% of this huge amount is sea-water, or salt water. Man can only drink and use the other 3% fresh water.【T17】______ , because some of it is in the form of icebergs and glaciers. Even worse, some of it has been polluted.
    At the moment, his small amount of fresh water is still enough for us. However, our need for water is increasing rapidly. Only if we take steps to deal with this problem now, can we avoid a severe worldwide water shortage later on. One of the useful steps we can take is to stop unlimited use of water.【T18】______ , however, would have a bad effect on agriculture and industry.
    In addition to stopping wasting our precious water, one more useful step we should take is to develop ways of reusing it.【T19】______ , 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. But it is possible to pipe water that has been used to a purifying plant. There it can be filtered and treated with chemicals【T20】______
【T19】

选项 A、 
B、 
C、 
D、 

答案D

解析 空白处前一句说的是“除了停止浪费我们珍贵的水资源,我们要采取的重要的一步就是发明重复利用水的方法”,空白处后面的句子说的是“但是只是小规模的”,所以这个空格内填入的应该与发明重复利用水源的方法有关,所以选项D“在这个领域内开展了很多实验”为正确答案。
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