Read the passage and fill in the blanks with proper words. (在短文的空格内填入适当的词，使其内容通顺，首字母已给，每空格限填一词): 6%
Deserts(沙漠) do not stay the same size. Sometimes they grow bigger. Sometimes they get s  . The world’s biggest desert , the 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, a  eat all the grass. Or people cut down the trees. This makes the soil weak. Weak soil lets the desert grow.
Why is it a p  ? People cannot grow food in the desert. People cannot build houses, hospitals, or schools in the desert. So people must l  their homes.
What can people do? They can plant trees. They can also f  less. These things make the soil stronger. Maybe the Sahara will stop g  . It’s a big problem. Many people must work together to solve it.