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: Physiology
[{'content': 'Velocity of blood flow in blood vessel is \nSelect and explain. \nA. Directly proportional to cross sectional area, B. Maximum is capillaries, C. Minimum in aorta, D. None of the above', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]