This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Surgery
[{'content': 'Most common cause of thoracic aortic aneurysm is \nSelect and explain. \nA. Atherosclerosis, B. Tuberculosis, C. Cystic degeneration, D. Syphilitic', 'role': 'user'}, {'content': "Answer: A \nExplanation: (A) AtherosclerosisDISEASES OF THE AORTA: ETIOLOGY & ASSOCIATED FACTORSAortic aneurysmAortic occlusion* Atherosclerosis* Atherosclerosis* Cystic medial necrosis* Thromboembolism* Tuberculosis* Aortitis* Syphilitic infection* Syphilitic aortitis* Mycotic infection* Rheumatic aortitis* Rheumatic aortitis* Takayasu's arteritis* Trauma* Giant cell arteritis* Aortic dissection * Cystic medial necrosis * Systemic hypertension * Atherosclerosis * Takayasu's arteritis * Giant cell arteritis", 'role': 'assistant'}]