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
National Family Health Survey is done every? 
Select and explain. 
A. 6 months, B. 1 year, C. 5 years, D. 10 years
B: 1 year
Answer: B: 1 year 
Explanation: Ans. is 'b' i.e., 1 year