A Pregnant Woman Tells the Nurse-Midwife, "I've Heard That If

A pregnant woman tells the nurse-midwife, "I've heard that if I eat certain foods during my pregnancy, the baby will be a boy." The nurse-midwife should explain that this is a myth, and that the sex of the baby is determined at what time?

A) At the time of ejaculation
B) At the time of fertilization
C) At the time of implantation
D) At the time of differentiation