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
Which of the following releases single wavelength of energy? 
Select and explain. 
A. QTH, B. PAC, C. LED, D. Argon lasers
D: Argon lasers
Answer: D: Argon lasers 
Explanation: None