I said D for the following question but I got it wrong, I know it's not B though because the disease isn't sex-linked and not C because people who get the disease are usually older (50's). Would the Answer be A then?

Question

Even though it's deadly the huntington's disease allele can remain in the population because:

A)The dominant allele sometimes reverts to a recessive form
B)it's sex linked to the male gamete and females don't carry the allele
C)people with the disorder often live long enough to reproduce
D)it's autosomal and can be masked by a codominant harmless allele

Answer 1

I don't see why it can't be C. Men may "have the disorder" (bad gene) even though symptoms do not show up until middle age, after reproduction.

Read "selection" of
http://evolution.berkeley.edu/evolibrary/article/medicine_05