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': 'In an endodontic file, D2 will be \nSelect and explain. \nA. At the tip of the instrument, B. At 2mm from the tip of the instrument, C. At 3mm from the tip of the instrument, D. At 16mm from the tip of the instrument', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]