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
Unpaired structures in the brain: 
Select and explain. 
A. Basilar artery, B. Vertebral artery, C. Middle cerebral artery, D. Anterior cerebral artery
A: Basilar artery
Answer: A: Basilar artery 
Explanation: Unpaired structure in the brain is basilar artery.