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
[{'content': 'This scalpel works on the principle of \nSelect and explain. \nA. Electricity, B. Laser, C. Radiofrequency, D. Ultrasonic waves', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Harmonic scalpel works on the principle of high energy ultrasonic waves (megahertz). Harmonic scalpel is used in liver resections and laparoscopic surgery.', 'role': 'assistant'}]