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': '70 year old man has abdominal pain with mass inabdomen. Angiography reveals aneurysm of aoa. Mostlikely cause is: \nSelect and explain. \nA. Trauma, B. Atherosclerosis, C. Syphilis, D. Congenital', 'role': 'user'}, {'content': 'Answer: B \nExplanation: . Atherosclerosis', 'role': 'assistant'}]