I'm confused, but the reason for why B is wrong is because it suggests the causal relationship is reversed (I.e., depression -> more sleep -> less LLA). But in the passage it's pointed out how depression itself is exhibited by less LLA. Indeed, only a correlation is seen, but couldn't we just be observing the causal relationship that the author claims? Insofar that even though we see that depression leads to less LLA, LLA is what causes depression in the first place?

I was stuck between C and D and ultimately picked C. But for D: can we not say that the immorality component of the conclusion is contingent on the mail being annoying, which in turn causes individuals to toss out the paper causing waste?