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
John Snow's discovery of cholera is an example of- 
Select and explain. 
A. Natural experiments, B. Spot map study, C. Randomized trial, D. Sho study
B: Spot map study
Answer: B: Spot map study 
Explanation: Ans. is 'b' i.e., Spot map study