Which hormone prevents degeneration of the corpus luteum?

hCG

Explanation:

The corpus luteum also called "yellow body" is the remaining of the ovarian follicle that has released a mature egg during a previous ovulation (it develops at each menstrual cycle). The corpus luteum is an endocrine structure which produces  of progesterone, estradiol and inhibin A.

If egg released during the ovulation becomes fertilized, human chorionic gonadotropin (hCG) secreted by the cells of the blastocyst signals the corpus luteum to continue progesterone secretion.The role of the corpus luteum is  to maintain endometrium of the uterus and provide an area rich in blood vessels for the zygote's development.