There is, however, much more to a desert than sand. In the deserts of the southwestern United States, cliffs (悬崖) and deep valleys were formed from thick mud that once lay beneath a sea more than millions of years ago. Over the centuries, the water dried up. Wind, sand, rain, heat and cold all wore away at the remaining rocks.

　　The faces of the desert mountains are always changing--very, very slowly--as these forces of nature continue to work on the rock.

　　Most deserts have a surprising variety of life. There are plants, animals and insects that have adapted to life in the deserr. During the heat of the day, a visitor may see very few signs of living things, but as the air begins to cool in the evening, the desert comes to life. As the sun begins to rise again in the sky, the desert once again becomes quiet and lonely.

　　1. Many plants may survive in deserts when_______.

　　A. the rain is spread out in a year

　　B. the rain falls only in a few weeks

　　C. there is little rain in a year

　　D. it is dry all the year round .

　　答案: A

　　指导：通过第一段内容可推出，此外作为中学生都应该有这样的常识，这题应是一个送分题。

　　2. Sand dunes are formed when_______.

　　A. sand piles up gradually

　　B. there is plenty of rain in a year

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