[求助]feifei-39

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?

答案：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。

 Choice C 里, 解释说题干没定义, 但我看题干有叙述到.
 不知是否有哪位大大知道choice C 错的原因为何?
      

 Choice C 里, 解释说题干没定义, 但我看题干有叙述到.
 不知是否有哪位大大知道choice C 错的原因为何?
      

不好意思~ 帖子没贴齐~

(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

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。

Choice C 里, 解释说题干没定义, 但我看题干有叙述到.
      

不知是否有哪位大大知道 choice C 错的原因为何?
    

原文说Q这个咚咚，离地球500M远，发出的光是多于90个太阳的光，能活100M年（简单翻译了~~）

选项说 在地球上看起来和Q一样亮的物体一定是发出了比90个太阳还多的光

但这个物体和地球的距离 未知，比如说在地球上看来相同亮度时，物体离地球的距离和它的实际发光有下列关系500M===90个太阳，250M===45个太阳 如果一个物体在250M处，发出45个太阳的光度，但和500M处90个太阳的光度在地球上看起来都是一样的，所以这个选项就错了。

you missed one more premised stated:"For anything that far away to appear from Earth the way quasars do"

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

c just mentioned as bright as, there r many stars bright as q, but nearer than it is to earth

see?

恩 明白了

C和D都只是说到了Q的一个方面：光亮或者距离。

类似你对c的解释，d的错误在于，只是说到和earth的距离与 Q到距离一样远 的东西不能exist 超过100M，显然就错误了。

如果满足Q，应该看得见，但是不存在了。