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
Ovulation is primarily caused by preovulatory surge of: 
Select and explain. 
A. Estradiol, B. Luteinizing hormone, C. Progesterone, D. Follicle stimulating hormone
B: Luteinizing hormone
Answer: B: Luteinizing hormone 
Explanation: 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