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: Medicine
[{'content': 'Most common site of aortic dissection - \nSelect and explain. \nA. Ascending aorta, B. Arch. of aorta, C. Descending aorta, D. Abdominal aorta', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]