Final answer:
The corpus luteum gland secretes progesterone. Progesterone targets the endometrium and causes it to thicken.
Step-by-step explanation:
The gland that secretes progesterone is the A) Corpus luteum. The target tissue of progesterone is the endometrium, which is the lining of the uterus. The effect of progesterone on the endometrium is to thicken and prepare it for potential implantation of a fertilized egg.