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': 'Circulus arteriosus is formed by \nSelect and explain. \nA. Anterior communicating artery., B. Basilar artery., C. Anterior, posterior cerebral and posterior communicating artery., D. All of the above.', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Circulus arteriosus or "circle of Willis" is a anatomical peculiarity of cerebral arteries.\nIt is formed by\n• Anteriorly by anterior communicating artery.\n• Posteriorly by basilar artery.\n• On each side by anterior cerebral, posterior cerebral, posterior communicating and internal carotid arteries.', 'role': 'assistant'}]