This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Female Reproductive System, Subject name: Physiology
[{'content': 'Which of the following is true during the 12-hour period preceding ovulation? \nSelect and explain. \nA. A surge of LH is secreted from the pituitary, B. The surge occurs immediately after the formation of the corpus luteum, C. The surge is followed immediately by a fall in the plasma concentration of progesterone, D. The number of developing follicles is increasing', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ovulation will not take place unless a surge of LH precedes it. Immediately prior to ovulation, the number of follicles is decreasing due to normal attrition of all but one follicle, and consequently estrogen synthesis by the ovary is decreasing. Progesterone synthesis is stimulated by the LH surge.', 'role': 'assistant'}]