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 number 12 in a 3 unit formula 12-6-8 indicates the blade is \nSelect and explain. \nA. 12 mm in length, B. 1.2 mm in length, C. 12 mm in width, D. 1.2 mm in width', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]