39. 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.

为什么这个是E呢？

离地球很远的quasar为了发出能在地球上看到的光，需按一定的比率燃烧 ，这些（为了产生能在地球上能看到的光的）quasar为了发光而100million years后就耗尽了（没了），而这些光达到地球时间需要 at least 500 million years ，所以E对。

(翻译没理顺，能看懂意思吧)

不是牛人，发表下看法。

  这种题G里也有几道，出题思路是这样的，情况A，然后给出条件1与A的条件比，最后反对条件1.推出情况A.

那个90MY跟100，没什么太多的区别。找到这种题的感觉就OK。不要过于在意细节