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': 'Normal pressure in superficial venous system of leg while walking is \nSelect and explain. \nA. 80 mmHg, B. 60 mmHg, C. 50 mmHg, D. 30 mmHg', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Pressure in superficial venous system decreases to 30 mmHg while walking as blood flows from superficial to deep veins.', 'role': 'assistant'}]