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
Frequency of ultrasonic preparation is: 
Select and explain. 
A. 20,000 - 25000 cycles/ sec, B. 5000 - 15000 cycles/ sec, C. 30000 - 40000 cycles/ sec, D. 1500 - 6500 cycles/ sec
A: 20,000 - 25000 cycles/ sec
Answer: A: 20,000 - 25000 cycles/ sec 
Explanation: Ultrasonic preparation: 

Consists of a peeso electric ceramic unit that generates ultrasonic waves which activate a magnetostrictive hand piece.
The 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.
NaOCI is used as irrigant solution.
Increased thermal and mechanical ability of the irrigating solution removes debris and tissue effectively and removal of smear layer is also efficient.