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': 'A patient known to have mitral stenosis and atrial fibrillation, presents with acute onset of weakness in the left upper limb which recovered completely in two weeks. The most likely diagnosis is: \nSelect and explain. \nA. Transient Ischemic Attack, B. Ischemic stroke, C. Hemorrhagic stroke, D. Vasculitis', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ischemic stroke', 'role': 'assistant'}]