六、任务型阅读。〔人与自然——自然生态〕
Today more than 20% of the land is desert, and this is growing. There is a picture, for example, from a cave in Algeria(阿尔及利亚). It shows cows and people. The area was very green, and plants and grass grew there. Many types of animals lived there. The picture is more than three thousand years old. Today, the cave is in a desert. Why are the deserts growing? There are three main reasons.
One reason is climate. The climate changed and rain did not come every year. The sun was very hot and all the water in the soil disappeared(消失).
Another reason is animals. For hundreds of years, people who lived near deserts kept goats. Goats like eating plants. They ate the plants, and there weren't any plants to stop the wind. When the wind blew, it blew all the good soil away. Soon, there wasn't any good soil and it was very difficult for plants to grow.
The third reason is people. People cut down trees, so no trees stopped the wind. Also, in some countries, people wanted to make electricity. They changed the direction of the rivers and they built dams(水坝). This changed the direction of the underground water in other countries.
In many places this is a very big problem. We have to be very careful about what we do to nature.
根据短文内容，回答问题。每题答案不超过6个词。
1. How much land today is not desert?
2. When was the picture drawn?
3. What can stop the wind and keep the good soil from being blown away?
4. What do we have to be careful about?
5. What are the three main reasons for the growth of deserts?

1. Less than 80% of the land. 2. More than three thousand years ago. 3. Plants. 4. What we do to nature. 5. Climate, animals and people.