根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。
Snow is a subject of great interest to weather experts .       . One reason is that heavy amounts of snow fall in surprisingly small areas . Another reason is that a small change in temperature can mean the difference between snow and rain .
Just what is snow , anyway ? Snow is a form of frozen water .       . These crystals grow from water droplets in cold clouds . They usually grow around dust particles（颗粒）. All snow crystals have six sides , but they grow in different shapes . The shape depends mainly on the temperature and water levels in the air .
   . About two and one-half centimeters of rain has as much water as 15 centimeters of wet snow . About 76 centimeters of dry snow equals the water in two and one-half centimeters of rain .
Snowfall helps to protect plants and some wild animals from winter weather . Fresh snow is made largely of air trapped among the snow crystals .      .
Snow can also influence the movement of sound waves . When there is fresh , soft snow on the ground , the surface of the snow absorbs , or takes in , sound waves .      . Then , the snow’s surface will help to send back sound waves . Under these conditions , sounds may seem clearer and may travel farther .

A．Much of the water the world uses comes from snow .

B．It contains groups of ice particles called snow crystals .

C．It is difficult to predict where , when or how much snow will fall .

D．Under some conditions , these particles may grow larger and form solid pieces of ice .

E. Snow contains much less water than rain .
F. However , snow can become hard and flat as it grows older or if there have been strong winds .
G. Because the air has trouble moving , the movement of heat is limited .