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 a survey, some schools were selected randomly from which classes were selected randomly and then sections were selected randomly and from which students were selected randomly, which type of sampling method is this \nSelect and explain. \nA. Simple random, B. Cluster sampling, C. Stratified sampling, D. Multistage sampling', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]