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
[{'content': 'Which of the following are unpaired vessel in CNS-- \nSelect and explain. \nA. Anterior cerebral artery, B. Basilar artery, C. Posterior cerebellar artery, D. Posterior communicating artery', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Basilar artery \xa0is 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.', 'role': 'assistant'}]