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
[{'content': 'To assess the perfusion in a free flap, the best technique is: \nSelect and explain. \nA. Pulse oximetry, B. Laser Doppler velocitometry, C. Fluorescine and dermal flumetry, D. Prick test', 'role': 'user'}, {'content': 'Answer: D \nExplanation: "Clinical observation with prick test remains the gold standard for monitoring flap perfusion.', 'role': 'assistant'}]