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
Laser used in laser doppler flowmetry is: 
Select and explain. 
A. Argon laser., B. HeNe laser., C. CO2 laser., D. Nd:YAG laser.
B: HeNe laser.
Answer: B: HeNe laser. 
Explanation: 632.8nm HeNe laser is used which is near to IR laser.