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
Velocity of blood flow in blood vessel is 
Select and explain. 
A. Directly proportional to cross sectional area, B. Maximum is capillaries, C. Minimum in aorta, D. None of the above
D: None of the above
Answer: D: None of the above 
Explanation: None