This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Circulation, Subject name: Physiology
The vasodilatation produced by carbon dioxide is maximum in: 
Select and explain. 
A. Kidney, B. Brain, C. Liver, D. Hea
B: Brain
Answer: B: Brain 
Explanation: Inhalation of 7% CO2 increases cerebral blood twofold. Cerebral blood vessels are very sensitive to CO2 tension. Hepatic aerial system is sensitive to adenosine; it brings about vasodilatation. Adenosine is the most impoant vasodilator of coronary vessels. CO2, H+, K+, hypoxia also cause reactive hyperemia. NO, an endothelium-derived relaxing factor is an impoant vasodilator of renal aerioles.