The conclusion: For-profit colleges enroll a greater proportion of financially disadvantaged students than do non-profit colleges.

The evidence: Relative to non-profit colleges, for-profit colleges draw a disproportionate share of federal and state financial aid.

The assumption: The people receiving aid to go to for-profit colleges are financially disadvantaged. One would think so. That's the point of the aid. But it would be useful to know whether the colleges -- either type -- are engaging in fraudulent practices that result in people who are NOT financially disadvantaged getting aid. If, for example, we found out that 93% of the time, for-profits colleges are committing fraud, and non-profits commit fraud only 1% of the time, then that seriously weakens the conclusion. If it were the other way around, that would strengthen the conclusion. Choice B directly addresses this point.

You asked about Choice C. One warning sign with this choice is the word "number." The conclusion is about "proportion." Let's say that we do have Choice C's info, and we knew, for example, that 1 million for-profit students got aid and 2 million non-profit students got aid. (The evidence says that for-profits get a disproportionate share of aid, not that they get MORE aid.) This doesn't tell us which type of college enrolled a greater proportion of financially disadvantaged students. Even ignoring the possibility of fraud, is that 1 million number 10% of all for-profit students or 99%? There's too much missing info for this choice to be useful by itself.

I'm available if you'd like any follow up.