The fraternal birth-order effect refers to a factor associated with
a.) pedophilia.
b.) sexual dysfunction.
c.) erectile disorder.
d.) sexual orientation.

Sexual orientation

Explanation:

Sexual orientation is related to the concept in which you attracted and want to make a relationship. Sexual orientation is related to gay, lesbian, homosexual, bisexual, asexual, etc. It is different from identity and gender identity.

Gender identity does not mean that whom to you attracted but it is about what are your sexual identity such as male, female, etc. It explains that being a transgender does not mean that you are gay, lesbian, bisexual, asexual, etc. Sexual orientation means who you have been with and gender identity is about who you are.  

answer; i believe its (transgender);