The hormone that maintains the endometrium.

The correct answer is Progesterone

Explanation:

• The endometrium is the inner lining of the uterus, which thickens in preparation for the potential implantation of an embryo.
• Progesterone is the hormone primarily responsible for maintaining the endometrium, ensuring it is suitable for embryo implantation and supporting early pregnancy.
• Progestrone hormone is produced by the corpus luteum in the ovary after ovulation. Progesterone maintains the endometrium, making it receptive to implantation by an embryo and supporting early stages of pregnancy. If pregnancy does not occur, progesterone levels fall, leading to the shedding of the endometrial lining during menstruation.

Other Options:

• Estrogen: Estrogen is a hormone that plays a key role in regulating the menstrual cycle and the development of female secondary sexual characteristics. It helps in the initial thickening of the endometrium but does not maintain it.
• Relaxin: Relaxin is a hormone produced by the ovaries and the placenta. It plays a role in relaxing the ligaments in the pelvis and softening and widening the cervix during childbirth. 
• Androgen: Androgens are a group of hormones, including testosterone, that are typically associated with male traits and reproductive activity.