The correct answer is choice C. Estrogen. Estrogen is a hormone that is normally formed in the ovaries and is also made by the placenta during pregnancy to help maintain a healthy pregnancy. Estrogen helps the uterus grow to accommodate the growing baby and maintains a well-functioning uterine lining and placenta. Estrogen also plays a role in regulating other essential pregnancy hormones and in developing fetal organs such as the lungs, liver, and endocrine glands.

Choice A is wrong because hCG (human chorionic gonadotropin) is a hormone that is only made during pregnancy and is mainly responsible for maintaining the corpus luteum, which produces progesterone. hCG levels rise a lot during the first trimester and may cause nausea and vomiting, but it does not directly stimulate uterine growth or fetal organ development.

Choice B is wrong because progesterone is a hormone that is made by the ovaries and by the placenta during pregnancy. It stimulates the thickening of the uterine lining for implantation of a fertilized egg and prevents uterine contractions during pregnancy.

Progesterone also supports fetal growth and development, but it is not the main hormone for stimulating