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标题: feifei-39 请教! [打印本页]

作者: tests 时间: 2005-6-1 12:35
标题: feifei-39 请教!
Quasars---celestial

objects so far away that their light takes at least 500 million years to reach

Earth---have been seen since 1963. For anything that far away to appear from

Earth the way quasars do, it would have to burn steadily at a rate that

produces more light than 90 billion suns would produce. But nothing that burns

at a rate that produces that much light could exist for more than about 100

million years.

If the statements above are true, which one of the following must also be true on the basis of them?

(A) Instruments in use before 1963 were not sensitive enough to permit quasars to be seen.

(B) Light from quasars first began reaching Earth in 1963.

(C) Anything that from Earth appears as bright as a quasar does must
produce more light than would be produced by 90 billion suns.

(D) Nothing that is as far from Earth as quasars are can continue to exist for more than about 100 million years.

(E) No quasar that has ever been seen from Earth exists any longer.

答案是E，为什么？而且题干也不太明白

[此贴子已经被作者于2005-6-1 12:37:53编辑过]

作者: nickt 时间: 2005-6-1 15:22

题目:光用500M年到达地球,但产生这种光的星体活不过100M年.

E.从地球上看到的这个星球已经不存在了.

作者: xiaoniuren 时间: 2009-7-22 17:24
D

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