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 maximum head diameter of ISO Gatesglidden drill # 1 is equivalent to: \nSelect and explain. \nA. No 50 file at Do, B. No 40 file at Do, C. No 60 file at Do, D. No 80 file at Do', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]