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
Study of Natural history is with 
Select and explain. 
A. Ecological study, B. Longitudinal study, C. Cross - sectional study, D. All of the above
B: Longitudinal study
Answer: B: Longitudinal study 
Explanation: None