The process during which sex is formed during prenatal development is called

A) sexuality.
B) sexual differentiation.
C) gender development.
D) transsexual construction.

Sexual differentiation is the process during which the sex of an individual is formed during prenatal development. This involves the differentiation of the gonads into testes or ovaries, which then produce hormones that drive further development of male or female reproductive organs and secondary sex characteristics. The other options (A, C, D) are related to different aspects of sexuality and gender, but do not specifically refer to the process of sexual differentiation.