Deserts(沙漠)do not stay the same size (形状).Sometimes they grow bigger. Sometimes they get smaller. The world’s biggest desert, Sahara, is in Africa. Right now, the Sahara desert is growing fast. Why is the Sahara growing ? In some places , People farm too much.  In other places ,animals eat all the grass. or people cut down the trees. This makes the soil(土壤) weak. Weak soil lets the desert grow. Why is it a problem? people can not grow food in the desert. people can not build houses, hospitals , or schools in the desert . so people must leave their homes .They must live somewhere else. What can people do ? They can plant trees. They can also farm less. These things make soil stronger. maybe the Sahara will stop growing . It’s a big problem. Many people must work together to solve (解决) it? 小题1:What is the main idea ?(中心思想) A．The Sahara Desert is in Africa . B．Farming too much makes the soil weak. C．Big problem are caused (引起) by the growing Sahara desert. D．Planting trees will help the world. 小题2:The Sahara is growing .Which of these things is not a reason(理由)？ A．Building homes B．Farming too much C．Animals eating the grass D．Cutting down trees 小题3:What do we know about deserts ? A．Their size never changes B．They are caused by people C．They can make trouble for people D．They are all in Africa. 小题4:Planting trees can A．make the soil weaker B．help people farm less C．be good for the soil D．make the Sahara grow. 小题5:Stopping growing the desert A．is easy B．takes a lot of people C．is not a big problem D．is not important