The correct option is D Relaxin
Relaxin is a hormone secreted by the corpus luteum and the placenta. During later stages of pregnancy, relaxin helps to soften the ligaments in the pelvis. This relaxes the pelvis, and helps the body with the strain of pregnancy.
Activin and inhibin are hormones produced by the gonads. They regulate the secretion of FSH and GnRH, with activin upregulating it and inhibin inhibiting it.
Estrogen is a female sex hormone involved in the growth of ovarian follicles and the endometrium during the menstrual cycle, and the development of female secondary sexual characteristics.