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).
