This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Sleep Disorders, Subject name: Psychiatry
[{'content': 'What is normal sleep latency:- \nSelect and explain. \nA. 20 minutes, B. 120 minutes, C. 60 minutes, D. 90 minutes', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Normal Sleep latency is about 20 - 40 minutes Any sleep latency less than 8 minutes is abnormal and quite characteristic of Narcolepsy. REM latency is different from sleep latency, as it is the time taken to enter the first REM phase during sleep. This is about 90 minutes.', 'role': 'assistant'}]