Section B
Directions: In this section, you will hear 3 short passages. At the end of each passage, you will hear some questions. Both the passage and the questions will be spoken only once. After you hear a question, you must choose the best answer from the four choices marked A, B, C and D.
听力原文： Would the world really be so much better off if there were no dust？ The answer is in some ways, yes, in some ways, no. What is dust anyway？ It consists of particles of earth, or other solid matter, which are light enough to .be raised and carried by the wind. Where do these particles come from？ They might come from dead plants and animal matter, from sea salt, from desert or volcano sand and from ashes. For the most part, dust is not a very desirable or beneficial thing. But in one way, it helps make the world more beautiful. The lovely colors of the dawn depend to a great extent on the amount of dust that is present in the air. Particles of dust in the upper air reflect the sun's rays. This makes its light visible on earth an hour or two after sunset. But different colors which make up the sun light are bent .at different angles as they are reflected by the dust and water steam particles. Sunsets are red, because these particles bent the red rays of the sun in such a way that they are the last rays to disappear from view. Another useful function of dust has to do with ram. The vapor water in the air would not become a liquid very readily, if it did not have the dust particles serving as centers for each drop of water. Therefore, clouds, mist, fog and rain are largely formed of an infinite number of moisture particles of dust.
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A. Of course.
B. It depends.
Certainly not.
D. It is not mentioned.