I have a question for (D). What if we negate (D): If a study CANNOT reliably determine the causes of those subjects' present characteristics, thena study of human subjects use NOT only accurate reports about the subjects' pasts.

Not only use accurate reports = could be use accu and non-accurate reports at the same time? ≠ use non-accurate reports.

I am a little bit confused.... I know C is the correct AC tho...

I think what rules (A) out it "obligated". CEOs in a charitable organization is not "obligated" to make profit, but they should still maximizing profit so that they can serve better for the public goods.