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': 'The most common cause of embolic stroke \nSelect and explain. \nA. Non rheumatic atrial fibrillation, B. Carotid aery atherosclerosis, C. Paradoxical embolism, D. LV aneurysm', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Non rheumatic atrial fibrillation No rheumatic atrial fibrillation leads to clot formation in left atrial appendage that can embolize to the brain leading to neurological dificits", 'role': 'assistant'}]