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': 'Ultrasonic devices are instruments for the removal of dentin from root canal walls have proved to be \nSelect and explain. \nA. Effective, B. Disappointing, C. Lethal, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]