How far is the sun from the earth? This is a question you have asked yourself since you began asking anything. In fact, for thou

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问题     How far is the sun from the earth? This is a question you have asked yourself since you began asking anything. In fact, for thousands of years astronomers【C1】______the same question. But they had no way of getting an exact answer【C2】______the sun was far, far away. Now with the use of radio telescope, they【C3】______give a very exact answer: the sun is 92,956,000 miles away from the earth.
    Can you imagine【C4】______that is?
    The airplane today travels【C5】______a speed of 700 miles an hour. Imagine that you were flying to the sun in this airplane. You could make no stops for rest,【C6】______for gas or oil, because there would be no place for you to stop. You would fly day and night at such a speed. Yet by the time you arrived, fifteen years would【C7】______
    The electric train can travel as fast as 110 miles an hour. If a railway could be built on a sunbeam, it【C8】______take the train nearly 100 years to【C9】______the sun. You would get very, very tired even if you lived【C10】______finish the journey.
    What a long way it is to the sun! Have you ever thought that the sun is as far away from us as that?
【C1】

选项 A、have asked
B、had answered
C、had been asking
D、have been answering

答案D

解析 根据上下文,这里表示千百年来。天文学家们一直在探究同一个问题。需要的时态应该是现在完成进行时。所以答案为D)。
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