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 deserts all the time. Scientists may not be able to change the deserts. Scientists think that people make deserts. People are doing bad things to the earth.
Some places on the earth don’t get much rain. But they still don’t become deserts. This is because some green plants are growing there. Small green plants and grass are very helpful(有帮助的) to dry places. Plants don’t let the hot sun make the earth even drier. Plants don’t let the wind blow the earth away. When a little bit of rain falls, the plants hold the water. Without plants, the land can become deserts much more easily.
Why can the land become deserts?

A．Some places don’t get much rain.

B．Plants don’t let the hot sun make the earth even drier.

C．People don’t keep the earth well.

D．Scientists haven’t learnt enough about the deserts.

Scientists want to          to make the deserts into good land again.

A．carry water	B．grow food
C．do nothing	D．study a lot

Why are green plants and grass helpful?

A．They can hold the water.

B．They can stop the wind from blowing the earth away.

C．They can keep the earth wet.

D．All the above.

After reading this, we learn that              .

A．it is good to get rid of (去除) the grass in the deserts

B．all places without much rain will become deserts

C．plants can keep (阻止) dry land from becoming deserts

D．it is better to grow crops（农作物）on dry land than to grow grass

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