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: Anaesthesia
Most potent cerebral vasodilator is 
Select and explain. 
A. B blocker, B. Nitro-glycerine, C. Hyper carbia, D. Nitroprusside
C: Hyper carbia
Answer: C: Hyper carbia 
Explanation: C i.e. Hyper carbia