This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Normal Menstruation, Abnormal Menstruation, Menopausal Physiology and forsight of conception, Subject name: Gynaecology & Obstetrics
Apoptosis can occur by change in hormone levels in the ovarian cycle. When there is no feilization of the ovum, the endometrial cells die because; 
Select and explain. 
A. The involution of corpus luteum causes estradiol and progesterone levels to fall dramatically, B. LH levels rise after ovulation, C. Estradiol levels are not involved in the LH surge phenomenon, D. Estradiol inhibits the induction of the progesterone receptor in the endometrium
A: The involution of corpus luteum causes estradiol and progesterone levels to fall dramatically
Answer: A: The involution of corpus luteum causes estradiol and progesterone levels to fall dramatically 
Explanation: The stimulus for the corpus luteum to continue its function of progesterone production is LH. This stops after the 10th day of its formation in the absence of pregnancy. As the corpus luteum involutes, the levels of estrogen and progesterone falls and leads to a withdrawl bleed due to absence of progesterone that was suppoing the estrogen primed endometrium. Once pregnancy ensues , the hCG made from the syncytiotrophoblast is the stimulator for continuous corpus luteum function till around 12th week of gestation after which the placenta takes over the function of pregnancy maintenance.