This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'Ovulation is primarily caused by preovulatory surge of: \nSelect and explain. \nA. Estradiol, B. Luteinizing hormone, C. Progesterone, D. Follicle stimulating hormone', 'role': 'user'}, {'content': "Answer: B \nExplanation: B i.e. LH A surge in LH secretion triggers ovulation and ovulation normally occurs about 9 hours after the peak of the LH surge at midcycle'Q", 'role': 'assistant'}]