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 tip diameter of a 245 bur used for conventional amalgam preparation is \nSelect and explain. \nA. 2 mm, B. 0.8 mm, C. 0.3 mm, D. 0.4 mm', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]