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
Most common cause of aneurysm of abdominal aoa is - 
Select and explain. 
A. Trauma, B. Atherosclerosis, C. Syphilis, D. Cystic medial necrosis
B: Atherosclerosis
Answer: B: Atherosclerosis 
Explanation: Ans. is 'b' i.e., Atherosclerosis