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
Incidence can be calculated by - 
Select and explain. 
A. Prospective study, B. Retrospective study, C. Case control study, D. Cross-sectional study
A: Prospective study
Answer: A: Prospective study 
Explanation: Ans. is 'a' i.e., Prospective study