In early Mesopotamian civilization, castor oil served not only as a la

Dear anurag16,

I'm happy to respond.

First, a little constructive criticism. I think this this color is exceedingly hard to see, so it would be best not to use it for anything you want seen.

If you think of the GMAT SC as a test of grammar, then the GMAT will trap you on question after question. The GMAT SC tests grammar, logic, and rhetoric all together, and SC mastery involves understanding the interplay of those three strands. If you focus exclusively on grammar, you will be lost on most of the harder questions. Here, you are making an argument about why (B) is grammatically correct. Of course (B) is grammatically correct---and that's precisely besides the point!

In this question, (B) is 100% grammatically correct, but it is not a good answer. Let's think about this. We are talking about uses of something. The most efficient way would be to say:
Castor oil was used as X, Y, and Z.
For whatever reason, the author wanted to highlight the contrast between the use as a "laxative" (something they put inside their bodies) with the other external uses. The author creates this contrast with the "not only . . . but also" structure. Thus,
Castor oil was used not only as a laxative, but also as Y and as Z.
That's still very elegant, and this is exactly what (C) does.
By contrast, (B) introduces a new clause for the third factoid, rather than simply include it on the same list. That's enormously clunky! New clauses should introduce something genuinely new, something that opens new logical ground. Why start an entire new independent clause for a single item that simply could be added to a list? That's an astonishingly poor rhetorical choice! There's no sense of elegance and style. This version is an absolute embarrassment compared to (C).

What's particularly tricky about this question is that the prompt also makes the same rhetorically disastrous choice, so this might make (B) appear not too bad. I am sure many GMAT takers focused exclusively on grammar fell for the trap of (B). Meanwhile, the hyper-literalist would see the change in (C) and think that's a "change in meaning," rather than simply the first appearance of high quality writing among the answer choices. These official questions are brilliant, and they are crafted at a very sophisticated level. The student who focuses purely on grammar will not fare well on these questions.

Does all this make sense?
Mike