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: Social & Preventive Medicine
[{'content': 'Whisper is \nSelect and explain. \nA. 10 db, B. 20 - 30 db, C. 30 - 50 db, D. 60 db', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]