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
[{'content': 'Study suitable for rare diseases ? \nSelect and explain. \nA. Coho study, B. Case-control study, C. Both of the above, D. None of the above', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Case-control study", 'role': 'assistant'}]