Once positioned in space, the Hubble Space Telescope will capture ligh

twenty times fainter - mean we need a than so A and B out.

now by ground-based instruments means we need passive voice in the underline area. So E out.

Now comparison is between two type of sources. So "than those" is meaningful. Undoubtedly D is the answer.

D it is.

We are comparing "sources"

"Hubble telescope will capture light from SOURCES 20 times fainter than those [SOURCES] that can be dectected by ground based instruments."

IMO..... D is the correct option. Fainter already shows that there is comparison between things..
fainter than seems good to me..
My answer D

When using a comparative adjective ("-er") "than" is required, so "compared to" is wrong.
Answer (A) & (B) are wrong

We need to be clear on what is/are being compared.
There are two nouns in this question that are eligible for comparison, light (that) and sources (those)
For which noun can we use the comparative adjective "fainter"?
Though,

"Fainter" makes more sense with light,
and the verb detected is more appropriate for "light" than "sources"

Answer choice (C) is wrong. Why? Answer choice (C) is missing subject for the "can be detected...." phrase.

(C) The Hubble Space Telescope will capture light from sources twenty times fainter than that [light] can be detected by ground-based instruments.
(C) The Hubble Space Telescope will capture light from sources twenty times fainter than that [light] that [light] can be detected by ground-based instruments.

(D) The Hubble Space Telescope will capture light from sources twenty times fainter than those [sources] that [sources] can be detected detected by ground-based instruments.

Correct answer (D)

Thanks

We are comparing "sources" not light here.

"Hubble telescope will capture light from sources 20 times fainter than those [sources] that can be detected by ground based instruments."
D is correct. Good question

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