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': 'The most common vein to get thrombosed is the - \nSelect and explain. \nA. Long saphenous, B. Short saphenous, C. Both, D. Posterior tibial', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]