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
Ultrasonic devices operate at 
Select and explain. 
A. 25-30 KHz, B. 35-40 KHz, C. 2-3 KHz, D. 5-10 KHz
A: 25-30 KHz
Answer: A: 25-30 KHz 
Explanation: None