日日人人_亚洲美女在线视频_av手机在线播放_国产大片aaa_欧美中文日韩_午夜理伦三级

Scientists are trying to make the deserts（沙漠）into good land again. They want to bring water to the deserts, so people can live and grow food. They are learning a lot about the deserts. But more and more of the earth is becoming desert all the time. Scientists may not be able to change the deserts. People are bad things to the earth.

Some places on the earth don’t get much rain. But they still become deserts. This is because some green plants are growing there. Small green plants and grass are very important to dry places. Plants don’t let the wind blow the soil（土壤）away. When a bit of rain falls, the plants hold the water. Without plants, the land can become a desert much more easily.

(     ) 1. Deserts________

A.      get very little rain

B.      never have any plants or animals in them

C.      can all be turned into good land before long

D.     both A and C

(    ) 2. Small green plants are very important to dry places because______

A.      they don’t let the sun make the earth even drier

B.      they don’t let the wind blow the earth away

C.      they hold water

D.     all of the above

(    ) 3. Land is becoming desert little by little because________

A.      plants can’t grow there

B.      there is not enough rain

C.      people haven’t done what scientists wish them to do

D.     scientists know little about the deserts

(    ) 4. Which is the main（主要的）idea of the first paragraph?

A.      Scientists know how to change desert into good land

B.      Land is becoming desert faster than scientists can change it back into good land

C.      If scientists can bring water to desert, people can live and grow food there

D.     More and more places are becoming deserts all the time

(    ) 5. After reading this, we can learn that _______

A.      plants can keep dry land from becoming desert

B.      it is good to get rid of the grass in the deserts

C.      all places without much rain will become deserts

D.     it is better to grow crops（谷物）dry land than to grow grass