75% of the earth’s surface is covered   1   water. However, the world is not only hungry but also thirsty for water. It seems    2   to you, isn’t it?

In fact, about 97% of water on the earth is sea water   3    salt water, which can’t be used directly. Man can   4   drink or use the other 3％of the fresh water    5    comes from rivers, lakes and underground. Some of it is in the form of icebergs（冰山）and glaciers(冰川).

As things stand today, this small amount of fresh water is still enough for us. On the other hand, because    6   number of people in the world    7    larger and larger, more and more fresh water is needed. That’s    8    water shortage becomes a big problem.

How can we    9   this problem? It’s both the scientists’ and    10   duty to find some ways to turn salt water into fresh water.