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
Most common cause of thoracic aortic aneurysm is 
Select and explain. 
A. Atherosclerosis, B. Tuberculosis, C. Cystic degeneration, D. Syphilitic
A: Atherosclerosis
Answer: A: Atherosclerosis 
Explanation: (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