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
Normal pressure in superficial venous system of leg while walking is 
Select and explain. 
A. 80 mmHg, B. 60 mmHg, C. 50 mmHg, D. 30 mmHg
D: 30 mmHg
Answer: D: 30 mmHg 
Explanation: Pressure in superficial venous system decreases to 30 mmHg while walking as blood flows from superficial to deep veins.