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': 'Number of air changes in a drawing room per hour should be at least \nSelect and explain. \nA. 5-Apr, B. 4-Mar, C. 3-Feb, D. 6-May', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]