This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Higher Functions, Subject name: Physiology
Which stage among the following has maximum contribution in sleep time of an adult? 
Select and explain. 
A. REM, B. NREM 1, C. NREM 2, D. NREM 3
C: NREM 2
Answer: C: NREM 2 
Explanation: In adults, the largest amount of sleep time is spent in stage 2 NREM sleep about 60 %; REM phases constitute 20-25% of total sleep time Stages 3 and 4 NREM about 15-20%, Stage 1 non-REM about 5%.