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: Psychiatry
Max duration of time spent is in NREM stage - 
Select and explain. 
A. I, B. II, C. III, D. IV
B: II
Answer: B: II 
Explanation: REM sleep occupies 20-30% of total sleep and NREM sleep occupies 60-70% (state I: 5-10%, stage II: 40-50%, stage III & IV : 15-20%).