There are deserts （沙漠） all over the world．Over half of Africa is desert．The United States has deserts in the southwest part of the country．In some places ，deserts are growing．This is a serious problem．Deserts destroy farmland and they also ruin （毁坏） land where animals live．When people can't grow food or find animals to eat，they have to leave their homes．

    Deserts spread（伸展） for different reasons．Sometimes nature causes this problem．Wind can move sand away from deserts and onto useful land．When there is no rain for a long time，many plants die and the land become a desert．However ，human also cause deserts to grow．This process（过程）is called "desertification"，and it happens in many ways．One way is caused by a lot of air pollution，which makes an area hotter．Hotter weather can reduce the amount of rain．Also，too many people in one area can damage the land．If they have many animals，their animals can also harm the land．When large animals like cows walk on soil too much，they turn it into dust．The wind easily blows this dust away．Trees help hold water in the ground．When people cut down a lot of trees，the water runs away and the soil is ruined．Plants stop growing in these places．

    All of these things can speed up desertification． To stop deserts from growing，people must think of ways to treat the land better．

1．What is the main idea of the passage?

    A．Where is the world's deserts are?

    B．How people live in deserts?

    C．The different reasons for growing deserts．

    D．How cows can stop deserts from growing?

2．Where are deserts found?

    A．Africa and Latin America．                  B．The United and China．

    C．On useful land．                       D．Across the whole world

3．Which is NOT a cause of desert growth?

    A．Little wind．                            B．Using land too much．

    C．No rain．                             D．Large animals．

4．How does humans cause desert growth?

    A．By causing pollution．                     B By eating only vegetables．

C．By keeping animals．                     D．By moving sand．

5．How can humans stop desert growth'?

   A．By using bicycles less．                     B．By raising more cows．

   C．By cutting down trees．                     D．By planting more trees．