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
Which of the following phase is characterized by presence of δ waves? 
Select and explain. 
A. A, B. B, C. C, D. D
C: C
Answer: C: C 
Explanation: C represents NREM 3 phase which is characterized by presence of δ waves. NREM 3 is also called as "deep sleep".