Unlike the virginal, whose single set of strings runs parallel to the

Hi CrushTHYGMAT,

A. If you've been led to believe that a relative (normally) cannot refer to a noun inside a prepositional phrase, there is no such (absolute) rule, but it'd be great to get more opinions on this. Sometimes, a test taker may prefer an approach that hides the actual complexity of an issue. Just to be clear, I'm not saying that this is a bad thing. It's up to you to decide whether you think this particular issue is important enough to warrant not taking any shortcuts.

B. If you've been told that the object of a preposition cannot be the subject of a clause in general, that's absolutely fine.

As always, it's good to be as precise as possible. We'll start once again with the fact that a noun that a relative refers to is never the subject of a verb inside a relative clause.

1a. The difficulty level of a question [that stumps me...]

As discussed earlier, the subject of the verb stumps is the relative that. Now, even though that points to a question (a noun inside the prepositional phrase of a question), we never say that a question is the subject of stumps. Why? Because if we look at a question as the subject of stumps, we may think that they form a subject-verb pair (a clause), like this:

1b. A question stumps me.

The problem is that (1b) is a complete sentence, whereas a question that stumps me is not. To make a mistake here is just asking for trouble, and an instructor should point such a mistake out.

2a. Some of the questions stump me.

Now, in this sentence, is some (of the questions) the subject, or is it just the questions? Clearly, not all the questions stump me, so we have an answer there. But if a student makes a mistake with a sentence like this, I don't always point it out. Most test takers can't give the GMAT more than an hour or two of their time every day, and instructors need to keep them focused on what really matters. In other words, I wouldn't really care about a problem here, unless it's related to something like subject-verb agreement.

2b. Of a question stumped me.

(2b) sounds really bad. We've forced the object of a preposition to act as the subject of a clause, which is just impossible. A mistake here is important, but if someone messes up on "the object of a preposition can't be the subject of an independent clause", it's most likely a silly mistake.

What I'd like you to check if whether you've taken (2) and applied it to (1) because you've been asked to look at the noun a relative points to as the "subject" of the verb inside the relative clause. If you have, then your approach is incorrect. You shouldn't look at the noun a relative refers to as the subject of the verb inside the relative clause.