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: Physiology
Arousal is most difficult in which stage of sleep - 
Select and explain. 
A. Stage 1 NREM, B. Stage 2 NREM, C. Stage 3,4 NREM, D. REM
C: Stage 3,4 NREM
Answer: C: Stage 3,4 NREM 
Explanation: Ans is 'c' i.e., Stage 3,4 NREM'In general, the ease of arousal from sleep parallels the ordering of the sleep stages, with NEM and stage 1 being the easiest for arousal and stage 4 the most difficult.