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
For calculation of incidence denominator is taken as- 
Select and explain. 
A. Mid year population, B. Population at risk, C. Total number of cases, D. Total number of deaths
B: Population at risk
Answer: B: Population at risk 
Explanation: Denominator for calculating incidence is population at risk.