This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
Which of the following are unpaired vessel in CNS? 
Select and explain. 
A. Anterior-cerebral aery, B. Basilar aery, C. Posterior- Cerebellar aery, D. Posterior-communicating aery
B: Basilar aery
Answer: B: Basilar aery 
Explanation: Basilar aery is single unpaired vessel, formed by right &left veebral aeries at lower border of pons, Ref: Gray's40e/p-262