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 an aortic aneurysm is - \nSelect and explain. \nA. Syphilis, B. Marfan's syndrome, C. Atherosclerosis, D. Congenital", 'role': 'user'}, {'content': 'Answer: C \nExplanation: An aneurysm \n\nAn aneurysm is a localized abnormal dilatation of a blood vessel or the wall of the heart.\nWhen an aneurysm is bounded by the true arterial wall, it is called a true aneurysm.\nWhen wall\xa0is ruptured and there is a collection of blood outside the vessel wall (extravascular hematoma) that is freely communicating with vessel wall false aneurysm. Most common cause of a false aneurysm is posted myocardial infarction rupture.\nAn aneurysm due to an infection that causes weakening of vessel wall → mycotic aneurysm.\nThe two most important causes of an aortic aneurysm (not only abdominal part but in any part of the aorta) are atherosclerosis and cystic medial degeneration of arterial media.', 'role': 'assistant'}]