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
A 40 year old male patient came for routine dental checkup. Patient gives history of root canal treatment with 17 and 27 done using excimer. This type of lasers are: 
Select and explain. 
A. Special infrared lasers​, B. Special ultraviolet lasers​, C. Special visible light lasers, D. Special blue light lasers​  ​
B: Special ultraviolet lasers​
Answer: B: Special ultraviolet lasers​ 
Explanation: The lasers range from long wavelengths (infrared), through visible wavelengths, to short wavelengths​ (ultraviolet). Excimers are special ultraviolet lasers.​