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
Which structure corsses the esophagus at 25 cm from the incisor teeth-a) Arch of aortab) Bifurcation of tracheac) Lt. bronchusd) Left subclavian artery 
Select and explain. 
A. a, B. bc, C. ac, D. b
C: ac
Answer: C: ac 
Explanation: None