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  3. The old belief that the universe never changes is quite wrong. Even before the invention of the telescope, astronomers noticed t

The old belief that the universe never changes is quite wrong. Even before the invention of the telescope, astronomers noticed t

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问题    The old belief that the universe never changes is quite wrong. Even before the invention of the telescope, astronomers noticed that bright stars suddenly appear in the sky, and then later disappear.【R1】______In fact we now know that they are really old stars which are slowly dying. A recent case of a nova occurred in 1918, and one of the few people who saw this was the American astronomer Edward Barnard. He was driving along in a car, occasionally looking up into the sky. Suddenly he noticed a star that he had never seen before, and exclaimed, "That star should not be there!" He was in fact watching the explosion of a nova.
  【R2】______As they do so, they let out huge clouds of material. Sometimes as large as the earth, and these explode into space at a speed of about 8, 000, 000 kilometers per hour. When this happens, the hotter parts of the star become visible, and this is why novae are so bright. Although the explosions are huge on a human scale, they only consume a small part of the dying star’s energy.
  【R3】______Indeed, there are even some stars which explode once a fortnight.
   There are other old stars which do not die slowly, but are completely destroyed by one great explosion.【R4】______The explosion of a supernova is equivalent to about a million, million, million, million hydrogen bombs going off at the same time. Just before the explosion the star’s density become very great and it spins at a very high speed. A matchbox of material taken from the star at that time would weigh about 1,000 tons, and the star would be turning at about 16,000,000 kilometers per hour.【R5】______One supernova which Chinese astronomers observed in 1054 can still be seen by us today. It has been shining for at least nine hundred years.
   A. Novae are old stars which are slowly dying.
   B. They are known as " supernovae."
   C. The death is a slow one, and the star may continue to explode for thousands of years.
   D. The explosion of a supernova is like a cosmic bomb.
   E. The explosion itself occurs suddenly, in the space of a minute, but the supernova continues to shine long after the event.
   F. These stars were called "novae" because they were thought to be new.
【R3】
选项
答案C
解析 本题的答题关键是空格的后一句：确实，有些恒星会每两周爆炸一次。这说明前文应该提及有些恒星在衰落的过程中可能会经历多次爆炸。因此选项C为最佳答案。
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