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: Pathology
[{'content': 'Most common cause of aoic aneurysm is ? \nSelect and explain. \nA. Atherosclerosis, B. Syphilis, C. Trauma, D. Congenital', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Atherosclerosis", 'role': 'assistant'}]