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
[{'content': 'Deep sleep is characterized by \nSelect and explain. \nA. α, B. β, C. δ, D. θ', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Deep sleep or NREM 3 is characterized by presence of\xa0δ waves\xa0→ Frequency 0-4 Hz.\nHence, NREM 3 is also called slow wave sleep.', 'role': 'assistant'}]