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
Number of air changes in one hour in a drawing room should be not less than 
Select and explain. 
A. 3, B. 2, C. 4, D. 5
B: 2
Answer: B: 2 
Explanation: None