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