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: Unknown
This scalpel works on the principle of 
Select and explain. 
A. Electricity, B. Laser, C. Radiofrequency, D. Ultrasonic waves
D: Ultrasonic waves
Answer: D: Ultrasonic waves 
Explanation: Harmonic scalpel works on the principle of high energy ultrasonic waves (megahertz). Harmonic scalpel is used in liver resections and laparoscopic surgery.