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: Surgery
[{'content': 'Most common cause of aneurysm of abdominal aoa is - \nSelect and explain. \nA. Trauma, B. Atherosclerosis, C. Syphilis, D. Cystic medial necrosis', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Atherosclerosis", 'role': 'assistant'}]