Multiple answers seem to fit

@sarahpretzel, Great question. There are actually two principles in the stimulus. The first tells us that if you don't believe an act of apparent generosity was performed out of selfless motives, then don't praise said generosity. The second tells us that if you don't believe an apparent act of selfishness was performed out of self interest, then you should not condemn said apparent selfish actions. (B) says, "It was correct for Sarah not to praise Michael for being charitable when he told her that he donates a tenth of his income to charity, since she guessed that he only told that fact in order to impress her." The problem with (B) is that in order for the first principle from the stimulus to actually work, the person who isn't praising has to believe that the act wasn't performed out of selfless motives. In (B), Sarah is merely guessing, so (B) doesn't conform to the first principle stated in the stimulus. (D) says, "Daniel was right not to praise Margaret for offering to share her house with a visiting French family, since he believed that she made the offer only because she hoped it would be reciprocated by an invitation to use the family's apartment in Paris." (D) conforms nicely to the first principle in the argument. Daniel believed that Margaret didn't perform the action out of a selfless motive because he thought she was just trying to get to stay in the family's apartment in Paris. (D) concludes that he was right not to praise her, and this matches up nicely with the first principle from the stimulus. (D) is the correct answer choice. Does this make sense? Let us know if you have any more questions!

So the correct answer is because Daniel believed instead of guessing?

I dont think so, I think that its right because it matches what the principle in question was