This is a comparison question. Solving it relies on understanding how the prepositions 'than' and 'as' are used in comparisons.

Comparisons either compare two things that are equal or unequal in respect to a certain trait. We use 'than' for unequal comparisons, and 'as...as' for equal comparisons.

Unequal: London is more expensive than Liverpool.
Equal: London is as expensive as Paris.

As you can see in the question below, the comparison is an unequal comparison: lightweight black holes have less mass than middleweight black holes. The comparison must use than - this eliminates A and B.

What about C, D, and E - all of them use 'than'?

It is easy to see that of the remaining answer choices, C is the most concise. D and E are wordy and create more confusion by introducing the pronoun 'it' unnecessarily.

Yes, that is true. Both the clauses are modifying the subject of main clause.
_________________

Hi nks2611 ,

You got confused man. When we have two independent clauses, they must be joined with comma + SANAM. But it is not true the other way.

What I mean is : if you are saying "we have a comma + SANAM, it MUST have an independent clauses joined together" is not correct.

Let's talk about this question:

IC: A middleweight black hole weighs in at roughly 500 solar masses,

DC 1 : hundreds of times more massive than the lightweight black holes produced by the collapse of individual stars
DC 2 : thousands or even millions of times less massive than the heavyweight giants that lurk in the centers of galaxies.

The two Dependent clauses here are showing the contrast by using the word "but".

Both these Dependent clauses are modifying a middleweight black hole.

I hope that makes sense.
_________________

Yeah, I meant the same. Got confused. Thanks Skywalker18
_________________