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: Anatomy
Which of the following are unpaired vessel in CNS-- 
Select and explain. 
A. Anterior cerebral artery, B. Basilar artery, C. Posterior cerebellar artery, D. Posterior communicating artery
B: Basilar artery
Answer: B: Basilar artery 
Explanation: Basilar artery  is single unpaired vessel, it is formed by right and left vertebral arteries, at lower border of pons and ends at upper border of pons by dividing into right and left posterior cerebral arteries.