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 key to occlusion is: \nSelect and explain. \nA. Maxillary permanent first molar, B. Maxillary permanent second molar, C. Maxillary primary first molar, D. Maxillary primary second molar', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]