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': 'Frequency of ultrasonic preparation is: \nSelect and explain. \nA. 20,000 - 25000 cycles/ sec, B. 5000 - 15000 cycles/ sec, C. 30000 - 40000 cycles/ sec, D. 1500 - 6500 cycles/ sec', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ultrasonic preparation: \n\nConsists of a peeso electric ceramic unit that generates ultrasonic waves which activate a magnetostrictive hand piece.\nThe hand piece produces movements of the shaft of the file between 0.001 to 0.004 inches in a frequency of 20,000 — 25,000 / sec.\nNaOCI is used as irrigant solution.\nIncreased thermal and mechanical ability of the irrigating solution removes debris and tissue effectively and removal of smear layer is also efficient.', 'role': 'assistant'}]