The world is not only hungry,and it will also be thirsty for water.About 97% of the water on the earth is sea water,or salt water.Man can only drink or use the other 3% of the fresh water which (37)___(come) from rivers,lakes and underground.On the other hand.Because the number of people in the world (38)___(become) larger and larger,more and more fresh water (39)___(need).So water shortage(短缺) becomes a big problem.
How can we work out the problem?Scientists (40)___(find) some ways to turn salt water into fresh water.One important way is(41)___(boil) sea water with high heat until vapor 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.We hope scientists (42)___(try) other ways to get the freshest water for the least money as soon as possible.