Top Law Schools

Got this question right but wanted to confirm two things. Does the first sentence function as background or support? And can we conclusively arrive at (D) because this is the contrapositive of the assumption that would directly link the support to the conclusion?

First sentence is just background - unnecessary to the argument.

I think you're close enough to the explanation for D that I don't want to go into a long explanation that might confuse you. But, suffice to say, D is right because it tells me that traits that always show up in T/C don't show up in S/R, letting me say that T/C can't be classified as S/R. They're mutually exclusive.

Thank you for helping me with my questions!