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': 'For large country surveys the sampling method of choice is: \nSelect and explain. \nA. Multiple sampling, B. Multiphase sampling, C. Cluster sampling, D. Multistage random sampling', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]