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: Anatomy
2nd constriction in oesophagus is seen at the following site - 
Select and explain. 
A. Where it crosses left main bronchus, B. Crossing of aorta, C. At pharyngoesophageal junction, D. Where it pierces the diaphragm
B: Crossing of aorta
Answer: B: Crossing of aorta 
Explanation: There are 4 esophageal constrictions. They are at 15cms, 22.5cms, 27.5cms and 37.5 to 40 cms, from the incisors. The second constriction is due to crossing of arch of aorta.