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Over millions of years ago, there were no deserts.
Now about three tenths of the Earth's surface{#blank#}1{#/blank#} deserts. The size of the world's deserts is
always {#blank#}2{#/blank#} (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 {#blank#}3{#/blank#} less than 50 cm of rain falls each year. The
Sahara Desert in Africa receives less than 1.5 cm a year. {#blank#}4{#/blank#} rain doesn't fall very often in deserts,
sometimes even for years, there can be heavy rain {#blank#}5{#/blank#}(sudden). Because they are dry, deserts
have wide changes in temperature each day. When the sun {#blank#}6{#/blank#}(go) up, it is very hot. At night, the
heat {#blank#}7{#/blank#} (receive) by the ground during the day {#blank#}8{#/blank#} (quick)
disappears (消失), and then it becomes very cold. Because{#blank#}9{#/blank#}the change, living in the desert is very
difficult. Man can make deserts, but they can also stop them from getting
larger and larger. Planting trees can prevent the sand from{#blank#}10{#/blank#}(spread).
