This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Normal Sleep, Subject name: Psychiatry
[{'content': 'How to differentiate between psychological and organic erectile dysfunction - \nSelect and explain. \nA. Nocturnal penile tumescence, B. PIPE therapy, C. Sildenafil induced erection, D. Squeeze technique', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e.. Nocturnal penile tumescence o One of the important method to distinguish psychogenic impotence from organic impotence is nocturnal penile tumsescence & early morning erection which are preserved in psychogenic impotence but not in organic cause of impotence.", 'role': 'assistant'}]