Long long ago, there were many trees on the mountains. In order to build houses and grow crops, people

cut down as many trees as they could. Soon all the trees have gone. The green hills have changed into

wasteland. As a result, sandstorms struck us from time to time. A lot of rich land has changed into desert,

leaving only sand. We suffered a lot from this. Now people have realized this and they go to the hill to plant

trees. In order to stop the wind from blowing the earth away, we have planted a lot of trees. We still need to

work harder to protect the environment.

答案不唯一