I received a PM asking me to comment on (a) how to tackle this question overall, and (b) why C is not acceptable. (Just a note to others: it's very useful, when posting a question, to detail what you do and don't understand about that question - it's easier for others to address your concerns if they know what your concerns are!)
This is definitely a tricky setup.
Among <big group>, <sub-group A> are less likely than <sub-group B> to X.
In the original sentence, X is a very complex clause with two sets of compound modifiers:
to be enrolled in <Y> imposing <modifier1> and requiring<modifier1> [to see <modifier 2> and spend <modifier2>]
The first set of modifiers modifies something before "imposing"; in addition, the "imposing" and "requiring" parts are parallel. The second set modifies something before "to see"; in addition, the "see" and "spend" parts are parallel.
So, let's start with: what are they modifiying? Nouns or clauses? Something, someone, or some clause is "imposing limits" and "requiring doctors" - what is it? It's the "insurance plans." That's a noun, so we want a noun modifier setup. Those -ing words that introduce modifying phrases or clauses indicate adverbial modifiers, not noun modifiers. Eliminate A. Scan the answer. Eliminate B for repeating the error.
You could also have started with the second set: what do they modify? They modify "doctors" and parallelism dictates that we read it as "require doctors to see more" and "<require doctors to> spend less time." The plan actually requires doctors to spend less time with patients? That meaning seems... off. More logically, spending less time would seem to be a consequence of having to see more patients in the first place.
C, D, and E all start with "that." "That" is an indicator of a noun modifier, so that's good. Let's check parallelism next, since we know compound modifiers need to be parallel. This is where it can get a little messy, because we also have "nested" modifiers. So go back and pick apart that meaning:
For simplicity, I'll just type one form of each relevant word. We've got: impose, require, see, spend. Should they all be parallel? Are only some parallel to others? What is each one talking about? Let's see.
The "insurance plans" both impose limits and require doctors, so those two should be parallel. Do the plans see more patients? Nope - the plan requires the doctors to see more patients. Do the plans spend less time with the patients? No - that's also the doctors. Do the plans require doctors to spend less time with patients? I hope not! The "spending less time" thing is a consequence of the previous requirement (having to see more patients).
C says: impose, require, and spend. This says that "insurance plans that impose limits, <insurance plans that> require doctors to see more patients, and <insurance plans that> spend less time with each. That last one has a nonsensical meaning - eliminate.
D says impose and require, spending. This says that "insurance plans that impose limits and <insurance plans that> require doctors to see more patients, spending less time with each." The ", spending" set-up indicates an adverbial modifier. Why are they spending less time with each? Not because they are doctors (noun) or because of the patients (noun), but because the doctors are required to see more patients (clause). Adverbial modifiers modify clauses. So this works.
E says impose, requiring and spending. This says "insurance plans that impose limits, requiring doctors to see more and spending less time with each." The ", requiring... and spending" pieces indicate a compoun adverbial modifier, so the fact that the plans impose limits should result in (a) doctors seeing more patients, and (b) someone (unclear who) spending less time with each. Are the doctors spending less time with the patients? Technically, (a) and (b) should be able to stand completely alone. If I strip out (a), I'm left with "insurance plans that impose stricter limits on medical services, spending less time with each." Who's actually spending less time? I don't know. Meaning is ambiguous - eliminate.
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Stacey Koprince
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(I'll remember it, of course, in order to answer other students' questions in future... but not for the test.)