graduating medical students

Great, I'm glad it's GMATPrep - that means we can discuss it.

First, the idiom is: "X is <4> times more likely than Y TO DO <something>"
The idiom is not "X is <4> times more likely than Y IN DOING <something>"

(You can substitute "as" for "more" up above and that still holds true.)

So, eliminate A. B doesn't say "in doing" but it says "who plan" - which is still not "TO DO" something, so eliminate B.

It is generally true that, as our strategy guide says, we should use the "as... as" construction when we are trying to relate two quantities by multiplication (as is the case in this problem). I should mention that there are rare exceptions, though (as there are for pretty much every grammar rule out there). So if you want some other ideas about how to eliminate, here you go:

In D, we've got two mixed-up comparison markers: "four times more likely" and "rather than." "Rather than" is comparing "minority graduates" to "other graduates" and "four times more likely" is comparing... "it" to "minority graduates"? No, that doesn't make any sense. "Minority graduates" to "other graduates"? Yes, that makes sense... but those two already have "rather than" as a comparison marker. Why do we have both?

No good reason, really, so eliminate D. D also, by the way, introduces a pronoun "it" that doesn't refer to anything in the sentence. That's technically okay, because this "it" is similar to the "it" in the following sentence: "It's raining outside." But, in this case, we have another option (C) that manages to convey the necessary info without introducing this unnecessary "it" so the other sentence is preferable. (The OG, if this were an OG problem, would probably say that this construction is "awkward.") Finally "will plan to practice" is redundant. They "will practice" in future, or they "plan on practicing" in future. Both mean the same thing, so we don't need both "will" and "plan." (Not to mention: you can't conduct a survey on what people say they WILL plan to do, because that means they aren't currently planning to do it, so they don't even know that, sometime in the future, they WILL plan to do it. And if they are currently planning to do something in future, then they're already planning to do it - it's not that they'll start to plan to do it at some future date.)

Was E supposed to say "rather than"? Or did it really just say "than"? Either way, E exhibits the same problem as D. Eliminate. (Also, as someone noted above, "to plan to practice" is not a great construction. The test-writers will generally avoid "to INFINITIVE to" when possible.