What Have Twin Studies Told Us About Sexual Orientation

What have twin studies told us about sexual orientation?

A) Twin studies are clear in supporting that sexual orientation is influenced only by genetic factors.
B) Twin studies clearly do not support the idea that sexual orientation is influenced by genetics.
C) Although supporting a genetic influence on sexual orientation, twin studies do not rule out environmental influences as a contributor.
D) Twin studies have not been done in the matter of sexual orientation.