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 general, hand sharpening of instruments with\nunmounted stones is preferable to sharpening by motor - driven mounted stones because unmouted stones \nSelect and explain. \nA. have a finer grain, B. are less likely to alter the bevel, C. are easier to sterilize, D. wear away less of the instrument surface', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]