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': 'Recommended working speed for light speed instrument is: \nSelect and explain. \nA. 550-650 rpm, B. 1000-2000 rpm, C. 5000-10000 rpm, D. 150-250 rpm', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]