57. 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.问

(A) compared to those that can b detected

(B) compared to those they can detect

(C) than that can be detected

(D) than those that can be detected（D）D is best. those 指代sources

(E) than those detecting

怎么than后面不能指代light呢？感觉说faint的应该是light而不是resources啊，因为光可以说暗淡啊，怎么resources呢？

所以C不可以？

1) sources can be refer to an astro-body which can be modified by bright or faint

2) than should followed by a plural noun or pronoun in order to fit save level comparision, I don't think that can be used as plural noun

hope that helps

注意比较级的比较成分。

light from sources twenty times fainter 比较的是来源， 来源的光亮程度。所以后面也得是来源或者指代来源的词。