This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fluid, Electrolyte and Nutrition, Subject name: Surgery
[{'content': 'Best vein for total parenteral nutrition is: \nSelect and explain. \nA. Subclan vein, B. Femoral vein, C. Brachial vein, D. Saphenous vein', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Best vein for total parenteral nutrition is: subclan vein > internal jugular vein > femoral vein', 'role': 'assistant'}]