This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Medicine
Most common cause of spontaneous SAH 
Select and explain. 
A. Trauma, B. Aneurysm, C. AV malformation, D. Hypeension
B: Aneurysm
Answer: B: Aneurysm 
Explanation: *85%of SAH are caused by saccular or 'berry' aneurysms arising from the bifurcation of cerebral aeries paicularly in region of the circle of willis . Ref Harrison20th edition pg 2445