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).
