This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Pharmacology
[{'content': 'Main mechanism of combined OCP? \nSelect and explain. \nA. Feedback inhibition of pituitary (causing of LH surge), B. Change in camicalmues, C. Decreased motility and secretion of the fallopian tube, D. Prevent amputation', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A. Feedback inhibition of pituitary (causing of LH surge)The estrogen provides a negative feedback on the release of FSH and LH by the pituitary. The progestin inhibits LH release. Both synergize to inhibit MID cycle LH surge. As a result, ovulation does not occur. Interference with ovulation is the most common pharmacologic mechanism for preventing pregnancy', 'role': 'assistant'}]