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': 'Piezo electric scaler has a wavelength of: \nSelect and explain. \nA. 6000-9000 Hz, B. 9000-12000 Hz, C. 2000-30000 Hz, D. 20000-45000 Hz', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]