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: Pathology
Most common cause of hypehalamic hypogonadotrophic failure in men: AI 10 
Select and explain. 
A. Klinefelter syndrome, B. Noonan syndrome, C. Viral orchitis, D. Kallmann syndrome
A: Klinefelter syndrome
Answer: A: Klinefelter syndrome 
Explanation: Ans. Klinefelter syndrome