The world is not only hungry，but it is also thirsty for water．This may seem strange to you，since nearly 70 % of the earth's surface is covered with water．But about 97 % of that is sea water，or salt water．Man can only drink and use the other 3 % ——the fresh(清新的)water from rivers，lakes，underground，and other sources．And we can not even use all of that．Even worse，some of it has been made dirty．
However，as things stand today，this fresh water is still enough for us．But our need for water is becoming larger and larger quickly-almost day by day．Only if we take steps to do with this problem now can we get away from a serious world-wide 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 refusing it．Today in most large cities，water is used only once and then sent out into a sewer system(下水道系统)．From there it returns to the sea or runs into underground places．
But even if every large city reused its water，we still would not have enough．All we'd have to do to make use of sea water in the world is to remove(清除)the salt．If we take these steps we'11 be in no danger of drying up．
(1)
The world is thirsty for water because ________．
[ ]
A．
man hasn't got enough food to eat
B．
we haven't got enough fresh water
C．
only 70 % of the earth's surface is water
D．
more water is sent into sewer systems
(2)
The underlined word valuable means ________．
[ ]
A．
much and salty
B．
fresh and enough
C．
dear and useful
D．
clean and helpful
(3)
What should we do if we want to have enough fresh water？
(a)make full use of the sea water
(b)carry salt water into lakes or rivers
(c)do our best to use the water again
(d)try to save the fresh water as much as possible
(e)drink and use all the water on the earth's surface
[ ]
A．
(c)and(e)
B．
(a)and(d)
C．
(a)and(d)
D．
(b)，(d)and(e)
(4)
The best but the most difficult way to solve(解决)the water problem of the world is to ________．
