Can you tell us where you got this question? It doesn't sound much like an official GMAT question. (For one thing, choice "A" is not the same as the original sentence).
The rule about "which" is this: a modifier beginning with "which" should refer to the noun (or noun idea) that directly precedes it. "Or the noun idea" is what makes this concept tricky. I could say "the board of directors, which is meeting this afternoon, has to vote on several major issues." In this instance, we're not modifying "directors," but the whole noun idea of "board of directors." Here we have a prepositional phrase "of directors" that is modifying the bigger idea of "board."
In my experience, though, the GMAT doesn't try to get too tricky about which noun is being modified. They would never give you a sentence like this: "The cat on the table, which is big, belongs to my brother." Does the modifier "which is big" refer to the table? That's the closest noun, and it would make sense. Or could it refer to the cat? "On the table" might just be part of the noun idea "cat on the table," so maybe that's what we're talking about? It would be impossible to tell which one we're modifying, so the GMAT wouldn't do that to you.
In your example question, the modifier comes after "consultant." So the modifier could refer to "consultant," but that doesn't make much sense from a meaning standpoint. A consultant doesn't rest on an interpretation. So it must be that we're modifying the whole noun idea of "the argument of the consultant." It's not stylistically elegant, but it could be passable grammatically.
The reason that I think this question doesn't sound like a real GMAT question is that answer choice B is also grammatically correct. It works from a comparison standpoint: "Unlike the company's argument... the competitor's argument." The modifier structure is perfectly sound here, too - the modifier comes right after "argument," and that's what it's meant to modify. I think the writers are assuming that one person (the consultant) is more comparable to a single competitor, than a company is to a competitor. But this distinction is meaningless - we could compare either one. It's also highly unlikely that a real GMAT question would change the meaning of the sentence so drastically (whose argument is it - a team of consultants, a consultant, or a company?) from answer choice to answer choice.
Let me know if this helps.
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
