Answer: The correct answer for the fill in the blank is- A) Progesterone.
Progesterone is a female sex hormone that is produced by ovary ( through corpus luteum), adrenal gland, and placenta during pregnancy. It plays a significant role in pregnancy. It helps in the thickening of endometrium lining of uterus that is important for the successful implantation of the embryo.
It is also helps in maintaining healthy pregnancy by nurturing the developing embryo.