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 pulp vitality test which uses the principle of measuring the velocity of RBC in capillaries: 
Select and explain. 
A. Laser doppler flowmetry., B. Pulse oximetry., C. Both., D. None
A: Laser doppler flowmetry.
Answer: A: Laser doppler flowmetry. 
Explanation: None