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': 'Which structure corsses the esophagus at 25 cm from the incisor teeth-a) Arch of aortab) Bifurcation of tracheac) Lt. bronchusd) Left subclavian artery \nSelect and explain. \nA. a, B. bc, C. ac, D. b', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]