狒狒一道逻辑题求解！！！！！

ricky27 · 发表于 2013-10-19 06:23:15

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.

答案：E？为什么选E
思路：
A：可能足够sensative，只是没有观察到而已。
B：同样只是没有观察到而已。
C：没有定义与地球的距离。
D：没有定义亮度
E：原文实际认为现在看到的来自Quasars的光是500万年前发出的。而在400万年前这些类星体就已经燃尽不存在了。

这个题为什么选E？No quasar that has ever been seen from Earth exists any longer. 这里我想的是，既然不知道什么时候从地球上能观测到Quasars，那也就不知道它在地球上被观测了多久。假如是100年前才开始观测到的呢，即使光线travle了500万年才到这里，那么观测到这个星辰燃尽也应该是几百万年之后的事了，难道是我物理没学好？

狒狒一道逻辑题求解！！！！！

所属分类: GMAT考试

正在浏览此版块的会员 ()