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: Surgery
[{'content': 'What is the most frequent tooth to be impacted ? \nSelect and explain. \nA. Lower third molar, B. Upper third molar, C. Lower canine, D. Upper premolar', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]