Bill's facial hair is an example of a(n)
a) secondary sex characteristic.
b) primary sex characteristic.
c) gender conformity behavior.
d) within-group variation.

I assume here that we mean the thick, characteristic hair that does not appear in women (since women also have some thin and white facial hair) - this is something that appears only at puberty and it's a physical characteristics.

This is then an example of a secondary sex characteristics - the answer is A).

The first answer is b. then the second one is a