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': 'Problem of bias is maximum with - \nSelect and explain. \nA. Coho study, B. Case study, C. Case control study, D. Experimental study', 'role': 'user'}, {'content': "Answer: C \nExplanation: Ans. is 'c' i.e., Case control study", 'role': 'assistant'}]