Answer: Option a: progesterone
Explanation: After ovulation, empty follicle becomes corpus luteum which secrets hormone progesterone. Corpus luteum establishes pregnancy by releasing progesterone hormone after ovulation by making the uterus feasible for implantation by making it thick. Progesterone takes part in the development of endometrium for the stability of pregnancy and helps to feed the developing fetus. During the entire pregnancy, progesterone levels are maintained which doesn't allow more eggs to be developed. If the fertilization doesn't occur, the corpus luteum does not secret this hormone, means the level of this hormone becomes low and menstruation occurs.