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': 'Case-control studies are used for - \nSelect and explain. \nA. Study of common diseases, B. Finding multiple risk factors, C. Finding incidence rates, D. Finding relative risk', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]