根据短文内容及首字母提示填空，使其意思完整。

     Typhoon is a very big wind.It usually starts at s    l    in July, August and September.

     How does a typhoon h    2   ? In summer. when the sun heats down on the sea, the water gets hot.

Then the hot water evaporates (v.蒸发) and goes up into the a    3    . This makes the air hotter. When

the air gets warm enough, it starts to move h    4    up into the sky, and starts to move quickly, making

wind. The wind goes in circles, and it keeps moving higher in the sky. And when the wind moves faster

than 30  meters a second, a typhoon begins.

    Typhoons are very d    5   . When a typhoon  happens, it usually causes (引起) strong winds and heavy rain. We should be careful when a typhoon is coming.

1.             2.             3.             4.             5.