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: Dental
[{'content': 'The common first approach to test causal hypothesis is \nSelect and explain. \nA. Descriptive study, B. Case-control study, C. Cohort study, D. Randomized controlled trial', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]