题目内容：
根据短文内容，回答题。The world is not only hungry，but 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 seawater，____51____ salt water．Man can only drink and use the other 3％of the flesh water that comes from rivers，lakes，underground，and other ____52____ ．And we cannot even use au of that，because some of it is in the form of icebergs and glaciers．Even worse，some of it has been polluted．
However，as things stand today，this small amount of flesh water，____53____ is constantly being replaced by rainfall，is still enough for US．But our need____54____water is increasing rapidly almost day by day．Only if we take steps to deal with this problem now ____55____ a severe worldwide water shortage later on．A limited water supply would have a bad effect on agriculture and industry．Let me give you just one small example of ____56____ necessary water is to industry．Do you know that____57____ a single ton of steel，it takes about 9 1，000 liters of water?
We all have to learn how to stop ____58____ our precious water．One of the first steps we should take ____59____ to develop ways of reusing it．Experiments have already been done in this field，but only on a small scale．The systems that have been worked out resemble ____60____ used in spacecraft．
___________ A．or
B．but
C．and
D．also
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