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
[{'content': "Poirier's triangle is bound by all except: \nSelect and explain. \nA. Left bronchus, B. Arch of aorta, C. Left subclavian artery, D. Vertebral column", 'role': 'user'}, {'content': "Answer: A \nExplanation: Thoracic duct is identified within Poirier's triangle which is formed by arch of aorta, left subclavian artery & vertebral column.", 'role': 'assistant'}]