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
[{'content': '2nd constriction in oesophagus is seen at the following site - \nSelect and explain. \nA. Where it crosses left main bronchus, B. Crossing of aorta, C. At pharyngoesophageal junction, D. Where it pierces the diaphragm', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 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.', 'role': 'assistant'}]