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: Surgery
To assess the perfusion in a free flap, the best technique is: 
Select and explain. 
A. Pulse oximetry, B. Laser Doppler velocitometry, C. Fluorescine and dermal flumetry, D. Prick test
D: Prick test
Answer: D: Prick test 
Explanation: "Clinical observation with prick test remains the gold standard for monitoring flap perfusion.