(A) fits the phenomenon hypothesis mold – it weakens the argument’s causal conclusion by providing an alternate cause for sunglass-wearing.

The stimulus gives us no reason to believe the doctors didn’t perform the usual tests.

The main narrative through which (B) resonates is that in the real world doctors do often dismiss valid health concerns brought to them by people they see as depressed or hypochondriacal. From that angle, (B) asks “what if the people in these studies actually had real health problems?”

You can spend a great deal of time puzzling out the implications that would have on the data, but all that speculation is cut short because, again, we have no reason to believe the doctors conducting the study neglected to perform the usual tests.

(C) attacks the argument’s overly general conclusion, pointing out that a correlation observed in gross foggy British hospitals might not persist across different climates.

(D) gives a bit of alternate cause energy and a bit of overgeneralization energy. It points out that a correlation observed in gross foggy British hospitals might not persist in other areas of the world, where people might wear sunglasses for fashion reasons instead of depression reasons.

(E) attacks the argument’s overly general conclusion (about how all sunglass-wearers across time and space are more likely to be depressed / hypochondriacal) by providing additional correlative evidence that undermines the claim. (“Check out these sunglass-wearers – they’re fine.”)