题目内容：

The UN passed a rule in the year 2004 to improve the quality of drink water and reduce deaths caused by drinking unhealthy water each year. The UN has already worked out the specific plan to reduce half of the number, that is, five thousand. The UN announced in the world there are about 1/6 of the world population can't meet the sanitation regulation of drinking water.

The water we drink and use is running short in the world. We all have to learn to stop wasting our quite limited water. One of the steps we should take is to find ways of reusing it. Experiments have already been done on this field. Today in most large cities, fresh water is used only once, then it runs into waste system. But it is possible to pipe the used water to a purifying(净化)factory. There it can be filtered(过滤) and treated with chemicals so that it can be used again , just as it were fresh from a spring. But even large cities purified and reused its water, we still would not have enough. Then we could turn to the oceans. All we would have to do to make use of seawater on earth is to get the salt out of it. This method has already been used in many parts of the world.

47. The way to stop wasting water is to ________ .

A. do experiments with water

B. purify the used water and reuse it

C. use fresh water once again

D. make use of seawater

48. The passage tells us how to reuse the used water. Which is the right order of the process?

a. to have the used water filtered b. to put chemical in it

c. to pipe it to the user

d. to pipe the used water to be purified in a factory.

A. dabc B. bcda C. bdca D. dcba

49. There wouldn't be enough water for us if we didn't ________ .

A. turn to the ocean for more water

B. reuse used water and make use of seawater

C. make fresh water from the seawater

D. take steps to reuse all water on earth

50. The word "it" underlined in the last paragraph refers to ________ .

A. the process of collecting salt from the ocean

B. the process of getting rid of the salt in seawater

C. purified water

D. seawater