551.     Once positioned in space, the Hubble Space Telescope will capture light from sources twenty times fainter compared to those that can be detected by ground-based instruments.

(A) compared to those that can be detected

(B) compared to those they can detect

(C) than that can be detected

(D) than those that can be detected

(E) than those detecting

答案是D，讨论区中说those 指代sources

但是从逻辑上讲fainter的，和被capture的不都应该是light嘛？后半句说其他instrument可以detect到，明显适合前半句说HST能够capture 到light对应

from sources是修饰light的，为什么fainter还是指代sources呢？

比较的是A twenty times fainter than B，

我想应该先清楚这个后置定语来修饰谁的，

如果是针对light的应该放到light后面的吧；

一上来，我也是马虎的选错了。。

后来我想想了哦：

C的错误是很明显的。。than that can be detected:

that 可以知道light，但是后面的can be detected ?应该是定语从句修饰前面的light。那么至少也因该是than light that can be detected..

正确的应该是than that that can be detected or than that detected by..