The world is not only hungry, but it is also thirsty for water．This may seem strange to you，since nearly 70 percent of the earth's surface is covered with water．But about 97 percent of this huge amount is sea water, or salt water．Man can only drink and use the other 3 percent-the fresh water from rivers，lakes，underground，and other sources．And we cannot even use all of that，because some of it is in the form of icebergs and glacier．Even worse，some of it has been polluted．
However，as things stand today, this small amount of fresh water is still enough for us．But our need for water is increasing rapidly-almost day by day．Only if we take steps to deal with this problem now can we avoid a severe worldwide water shortage later on．
We all have to learn how to stop wasting our valuable water．One of the first steps is to develop ways of reusing it．
Today in most large cities，water is used only once and then sent out into a sewer system．From there it returns to the sea or runs into underground storage tanks．But it is possible to pipe used water to a purifying plant．There it can be treated with chemicals so that it can be used again，just as if it were fresh from a spring．
But even if every large city purified and reused its water，we still would not have enough．All we'd have to do make use of the vast reserves of sea water in the world is to remove the salt．
If we take these steps we'll be in no danger of drying up．
56．The world is thirsty for water because we can only use percent of the water covering the surface of the earth．
A．3 B．more than 3 C．less than 3 D．97
57．Which of the following statements is NOT TRUE?
A．As things remain unchanging，this small amount of fresh water is still enough for us．
B．Our need for water is becoming larger and larger．
C．There will be no water shortage in the future．
D．We should take steps to deal with the water shortage problem．
58．To reuse water, we should ．
A．treat it with chemicals B．use it only once
C．send it out into a sewer system D．make it flow into underground tanks
59．In order to have enough water．we should also make use of ．
A．icebergs and glaciers B．sea water
C．rivers and lakes D．underground water
