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: Medicine
[{'content': 'Hemiplegia is most commonly caused by thrombosis of \nSelect and explain. \nA. Anterior cerebral artery, B. Middle cerebral artery, C. Posterior cerebral artery, D. Basilar artery', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]