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': 'For most effective cutting and long usefulness of a tungsten carbide bur, it should be \nSelect and explain. \nA. Rotating slowly before contacting the tooth, B. Rotating rapidly before contacting the tooth, C. Placed in contact with tooth before starting, D. Rotating rapidly before entering in to the oral cavity', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]