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: Dental
To study the incidence of caries in 10 yr old in a school which is best study design. 
Select and explain. 
A. Porspective, B. Retrospective, C. Cross sectional study, D. Cross over study
A: Porspective
Answer: A: Porspective 
Explanation: None