Snow falls in the Earth’s extreme North and South throughout the year. However， the heaviest snowfalls have been reported in the mountains of other areas during winter. Snow is even known to fall near the Equator (赤道)，but only on the highest mountains. Snow contains much less water than rain, but much of the water the world uses comes from snow. Melting snow provides water for rivers, electric power stations and agricultural crops. In the western United States, mountain snow provides up to seventy-five percent of all surface water supplies. Snowfall helps to protect plants and some wild animals from winter weather. Fresh snow is made largely of air trapped among the snow crystals (晶体). Because the air has trouble moving, the movement of heat is limited. Snow also influences the movement of sound waves. The surface of the snow takes in, or absorbs, sound waves. As snow grows older or if there have been strong winds, it can become hard and flat. Then, the snow，s surface will help to send back sound waves. Snow may be beautiful, but it can be deadly. It is responsible for the deaths of hundreds of people. Many people die in traffic accidents on roads covered with snow and ice or from being seriously stuck in the winter storm. Others die from heart attacks caused by too much physical activity out in the cold. People may not be able to avoid living in areas where it snows often. However, they can avoid becoming victims of snowstorms. People should stop driving and stay at home until the storm has passed. People living in these areas should carry emergency supplies in their vehicle. These include food，emergency medical supplies，and extra clothing to stay warm and dry. 小题1:Mountain snowfall _____.
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