Much of the water we use comes from snow. Melting snow provides water for rivers, electric power centers and agricultural crops. In the western United States, mountain snow provides up to 75% of all surface water supplies.
Snowfall helps to protect plants and some wild animals from cold, winter weather. Fresh snow is made largely of air trapped among the snow crystals. Because the air has trouble moving, the movement of heat is greatly reduced.
Snow also is known to influence the movement of sound waves. When there is fresh snow on the ground, the surface of the snow takes in, or absorbs, sound waves. However, snow can become hard and flat as it becomes older or if there have been strong winds. Then the snow's surface will help to send back sound waves. Under these conditions, sounds may seem clearer and travel farther.
Generally, the color of snow and ice appears white. This is because the light we see from the sun is white. Most natural materials take in some sunlight. This gives them their color. However, when light travels from air to snow, some light is sent back, or reflected. Snow crystals have many surfaces to reflect sunlight. Yet the snow does take in a little sunlight. It is this light that gives snow its white appearance.
Sometimes, snow or ice may appear to be blue. The blue light is the product of a long travel path through the snow or ice. In simple terms, think of snow or ice as a filter. A filter is designed to reject some substances, while permitting others to pass through. In the case of snow, all the light makes it through if the snow is only a centimeter thick. If it is a meter or more thick, however, blue light often can be seen.
小题1:How many functions of snow are discussed in the passage?
A．One
B．Two
C．Three
D．Four小题2:Why does snowfall help to protect plants from cold?
A．Because snow crystals contain heat.
B．Because snow crystals have air in them.
C．Because snow crystals are easy to blow away.
D．Because snow crystals send out heat when melting.小题3:It can be inferred that ______.
A．hard snow is better in protecting wild animals than fresh snow
B．fresh snow is better in sending sound waves than hard snow
C．fresh snow is better in taking in sound waves than hard snow
D．hard snow provides less water than fresh snow小题4:The color of snow and ice appears white because snow crystals________.
A．send back none of the sunlight
B．send back all of the sunlight
C．take in most of the sunlight
D．take in some of the sunlight
小题1:C
小题2:B
小题3:C
小题4:D
题目分析：本文给我们介绍了我们常见的雪的作用，及雪为什么会成白色。这里提到的它的作用有三点，一是雪给我们提供水源。二是雪能够给野生动植物防寒。三是雪能影响声的传播。
小题1:这是细节理解题。根据前三自然段可知雪能提供水源，能给野生动物和植物防寒，能影响声的传播，故选C。
小题2:这是细节理解题。根据Fresh snow is made largely of air trapped among the snow crystals. Because the air has trouble moving, the movement of heat is greatly reduced.因为雪里有空气，阻止热的运动。故选B。
小题3:这是推理判断题。根据When there is fresh snow on the ground, the surface of the snow takes in, or absorbs, sound waves. However, snow can become hard and flat as it becomes older or if there have been strong winds. Then the snow's surface will help to send back sound waves. Under these conditions, sounds may seem clearer and travel farther.因为新鲜的雪能够吸收声波，这就影响了声的速度，而硬的雪有利于声的传播，加快了声的速度。故选C。
小题4:这是细节理解题。根据Snow crystals have many surfaces to reflect sunlight. Yet the snow does take in a little sunlight. It is this light that gives snow its white appearance.雪的晶体有许多表面来反射阳光，雪就吸收了一些光，就是这种光让雪成白色。故选D。
点评：推理判断就是根据作者的意图和倾向来完成相关的问题。 根据你对文章的理解，来判断各个选项的正误。最重要的就是读懂句子的意思，找出文章的中心，这种阅读是深层阅读，但是你最重要的就是找出文章的中心意思，抓住主要句子和相关句子的意思就可以解决了，要注意题目中的一些关键词和文章中的句子的对比，尤其是一些转折词、连词等等。