请认真阅读下列短文，从短文后各题所给的A、B、C、D四个选项中，选出最佳选项。
A
If you travel by air across the center of Africa or South America, you fly over forests for thousands of kilometers. These great forests are the oceans of trees. There are full of thousands and thousands of different kinds of plants and animals.
However, the world's forests are getting smaller all the time. We are cutting down the trees because we need wood, and we need more farm land. Some people say that there will not be any forests like these in 20 or 30 years. what will happen if they disappear?
If we cut down our forests, a lot of plants and animals will disappear from the world. In a lot of places the new farm land will soon look like the old deserts. Crops will not grow there. It will not rain very often, and the weather will get very hot. Perhaps the climate of the world will change. This will be dangerous for everyone in the world. That is why we must take care of our forests.
