Answer: D. Bisexuality
Step-by-step explanation:
Simply put, a sexual orientation can be defined as the relation of genders in which a person is attracted to. Answers B, C, and arguably A discuss matters of one's own gender not necessarily one they are attracted too.
However, D. Bisexuality, discusses the act of liking both the male and female gender. And because it consequently involves the liking of other genders while not implying their own gender, the answer is D. Bisexuality.