5．
阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空。
Over millions of years ago, there were
deserts. Now about one fifth of the Earth's surface(be)
deserts. The size of the world's deserts is always(change).
Deserts can be hot or cold. The Australian Desert is a hot desert, while the
Gobi Desert in Mongolia is an example of a cold desert. Deserts are dry areas
where less than 25 cm of rain falls each year. The Sahara Desert in Africa
receives(little) than 1.5 cm of rain a year.rain
doesn't fall very often in deserts, sometimes even for years, there can be
heavy rain(sudden). Because they are dry, deserts
have wide changes in temperature each day. When the Sun goes,
it is very hot. At night, the heat(receive) by the ground during the day(quick)
disappears (消失), and then it becomes very cold. Becausethe
change, living in the desert is very difficult. People can make deserts, but
they can also stop them from getting larger and larger. Planting trees can
prevent the sand from(spread).
