15．　　　　　　 C。介词as表示“作为”，为正确选项。

18

You may think there is only sand in the desert of the world, __1__ it is not true. In the desert, as we know, there is a little __2__, but it is not __3__ for most plants. Still we can see some plants __4__ in the desert.

There is __5__ in some places in the desert. We __6__ these places oases. In the oases, there are villages and towns. People grow __7__ kinds of crops in the fields there.

People __8__ live outside the oases. They have camels, sheep and other animals. These animals depend __9__ the desert plants for their food and do not need __10__ water.

The __11__ are useful to the desert people in many ways. They eat the meat and drink the milk of the animals. They use the camels for carrying water, food, tents and something else.

The people of the desert have to keep moving from place to place. They must always look 　12　 grass or desert plants for their animals. When there is no more food for their animals, they move to __13__ place. The desert people are __14__. No man in the desert would ever refuse __15__ the people in trouble and give them food and water.

14．　　　　　　 D。think of表示“想起；认为”；think about表示“考虑”；think out表示“想出”；根据文章含义，答案应是D。

13．　　　　　　 A。learn后面接的是一个宾语从句，而且连接词在从句中做learn 的宾语，所以只能用what，因为that在宾语从句中是纯连词，只能起连接作用，不能做句子成分。

12．　　　　　　 C。know about表示“了解”，侧重于有关某人或某事的具体情况。

11．　　　　　　 A。用介词for+宾语表示“为人们做事”，故选A。

10．　　　　　　 D。

9．C。动词短语go through表示“经历……”。

8．D。该句句意为“自它诞生之日起，它的发展就非常迅速”，since在意思和时态上与主句呼应，为正确选项。

7．C。根据常识可知老式计算机庞大而笨重，故填large。

6．C。因为Enid是名字，故用called。