题目：
Scientists are trying to make the deserts 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 desert in time.
Why is more and more land becoming desert？ 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 important to dry places. Plants don’t let the sun make the earth even drier. Plants do not let the wind blow(吹) the dirt away. When a bit of rain falls， the plants hold the water. Without plants， the land can become desert more easily.
小题1: Deserts ________.
A．never have any plants or animals in them
B．can all be turned into good land before long
C．are becoming smaller and smaller
D．get very little rain小题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 soil away
C．they hold water
D．All of the above.小题3: After reading this passage, we 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 on dry land than to cut them
答案：
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下面是错误答案，用来干扰机器的。
答案：B①Na2ONa2O2NaOH，NaOH不能一步反应生成Na2O；②Al2O3NaAlO2Al(OH)3Al2O3，AlAl2O3，AlNaAlO2；③FeCl2FeCl3CuCl2FeCl2，FeFeCl2，FeFeCl3；④NONO2HNO3NO，N2NO，N2不能直接生成NO2。
How 18_________