In the late seventh century, in a dispute over whether the Prophet Muh

Dear ammuseeru,

I'm happy to respond.

To be honest, I am not impressed with this question at all. First of all, the GMAT would never pick so sensitive a topic. I could imagine that some devout Muslims might take offense that the name of God's holy Prophet, peace be upon him, appears in something a trivial as a practice question. All religions should be treated with the utmost of respect, and the official GMAT never touches these topics. Furthermore, I don't think the grammar is sound: I think the posted OA has problems--in fact, I think all five answer choices are wrong.

I think "carry on" is a sloppy casual way to say "continue"--the GMAT would never use this casual construction. Even (A) uses this. The structure "carry on and be the fourth caliph," in both (B) & (C) is even worse!! This makes it sound like two different activities. In American slang, "to carry on" means to have an extramarital sexual affair, so the possible implication to a native speaker's ears are absolutely scandalous! Arguably, (B) and (C) not only are wrong but verge on blasphemous. This questions has numerous shortcomings: its overall quality as a practice question is atrocious.

The word "whether" is perfectly fine with "should." Suppose there's a GMAT student named John. If we know John and know his struggles with math, we might make the factual statement.
John should study more GMAT Quant.
Suppose someone else doesn't know John as well, and wants to ask about this fact. That person might say:
I don't know whether John should study more GMAT Quant.
This can arise whenever our question ("whether") is about the nature of the decision ("should").

Does all this make sense?
Mike