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': 'Sonic system runs at \nSelect and explain. \nA. 2-3 KHZ, B. 25-30 KHz, C. 15-20 KHz, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]