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': 'Commonest cause of cerebral infarction is - \nSelect and explain. \nA. Embolism, B. Arteritis, C. Thrombosis, D. Cysticercosis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]