The world is not only hungry, it will also be thirsty for water. About 97% of water on the earth is sea water, or salt water. Man can only drink or use the other 3% of the fresh water(淡水)which comes from rivers, lakes and underground. On the other hand, because the number of people in the world is becoming larger and larger, more and more fresh water is needed. So water shortage becomes a big problem.

　　How can we work out this problem? Scientists have found some ways to turn salt water into fresh water. One important way is to boil(使達(dá)到沸點(diǎn)) sea water with high heat until vapor(蒸汽) rises, leaving the salt. In this way, a lot of fresh water can be made quickly.

　　But heating is not the only way to get fresh water. Other ways are tried,for example, digging deep wells, keeping rain water and preventing rivers from being polluted.

　　Which way is the best? To get the most fresh water for the least money is the best.

　　41. Where does the fresh water people need come from?

　　A. Sea water B. Rivers aid lakes C. Underground D. Both B and C

　　42. From this passage we know fresh water .

　　A. only comes from the rain B. can be used in many ways

　　C. can be found in many factories D. is needed by more and more people

　　43. The word 'shortage' in this passage means '_______' .

　　A. being enough B. being short of C. being short for D. being less

　　44. What is the writer mainly talking about in this passage?

　　A. The ways of getting fresh water.

　　B. How to use fresh water in our daily life.

　　C. A11 people in the world should save water.

　　D. Different ways of making water in different places.

　　45. Which of the following is true?

　　A. Hunger is the only problem in our world.

　　B. Water shortage is the only problem in our world.

　　C. Scientists don't want to spend money solving the water problem.

　　D. Scientists have been working hard and have made much progress in solving water problem.