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
Delta waves in EEG are 'seen in : 
Select and explain. 
A. Deep sleep, B. REM sleep, C. Awake with eyes open, D. Awake with eyes closed
A: Deep sleep
Answer: A: Deep sleep 
Explanation: A i.e. Deep sleep