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
[{'content': 'In physiology of the menstrual cycle, all are true EXCEPT ? \nSelect and explain. \nA. Ovulation follows 36 hours after the onset of LH surge, B. Follicular phase is constant, C. Withdrawal of endogenous progesterone results in endometrial breakdown and subsequent menstruation, D. Average cycle length is 21-35 days', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Menstrual cycle Follicular phase is variable. Luteal phase is constant FSH levels rise during ovulation Ovulation follows 36 hours after the onset of LH surge or 10-12 hours after LH peak Withdrawal of endogenous progesterone results in endometrial breakdown and subsequent menstruation Average cycle length is 21-35 days', 'role': 'assistant'}]