Question

4．Winter weather has returned to northern areas of the world．In much of the United States，winter means the return of snow．
Snow is a form of frozen water．It contains many groups of very small ice particles （颗粒）called snow crystals（晶体）．These crystals grow from water particles in cold clouds．They usually grow around a piece of dust．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．The shape of a snow crystal may change from one form to another as the crystal passes through levels of air with different temperatures．Snow contains much less water than rain．About 75 cm of snow has as much water as 2.5cm of rain．
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．However，when light travels from air to snow，some light is sent back，or reflected（反射）．Snow crystals have many surfaces to reflect sunlight．It is this light that gives snow its white color．
Much of the water we use comes from snow．Melting（融化） snow gives water to rivers and crops．Snowfall helps to protect plants and some wild animals from the cold．Fresh snow is made largely of air which is kept among the snow crystals．Because the air has trouble moving，the movement of heat is greatly reduced．However，snow is responsible for the deaths of hundreds of people in the United States every year．Many people die in traffic accidents on roads that are covered with snow or ice．
71．In the center of a snow crystal there isC
A．air       B．water      C．dust     D．sunlight
72．If fifteen centimeters of snow completely melts，the height of water will beA
A.0.5 centimeter   B.1centimeter   C.1.5 centimeters   D.15 centimeters
73．According to the text，snow looks white becauseC．
A．snow is actually white                
B．the ice particles are white
C．the reflection of light makes it look white 
D．there is a lot of air in the snow
74．How can snow protect plants from the cold？D
A．Snow gives them much heat．
B．Snow turns into water and waters them．
C．Snow makes them keep moving．
D．Snow contains air which has trouble moving．
75．What is the last paragraph of the text mainly about？C
A．Snow can give water to rivers and crops．
B．Snow can help crops keep warm in winter．
C．Snow has both advantages and disadvantages．
D．Snow is the cause of the deaths of many people．

Answer 1

分析 本文主要是告诉了我们雪的形状、用途、颜色及影响．

解答 71．答案 C 根据They usually grow around a piece of dust．可知，雪晶体的中心是尘埃，故答案为C
72．答案  A 根据About 75 cm of snow has as much water as 2.5cm of rain．可知，75厘米的雪融化成2.5厘米的水，那么15厘米的雪融化成0.5厘米的水，故答案为A
73．答案 C 根据Generally，the color of snow and ice appears white．This is because the light we see from the sun is white．可知，雪是白色的是因为反射的光的原因，故答案为C
74．答案 D 根据Because the air has trouble moving，the movement of heat is greatly reduced．可知，雪中含有空气，可以阻碍空气的流动，避免了热量的流失，故答案为D
75．答案 C 根据Snowfall helps to protect plants and some wild animals from the cold．及However，snow is responsible for the deaths of hundreds of people in the United States every year可知，雪对于这个世界既有有利的一面，也有不利的一面，故答案为C

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