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': 'During endotracheal intubation, unilateral breath sounds, no air heard entering the stomach and no gastric distension is suggestive of entry of the endotracheal tube into - \nSelect and explain. \nA. Right main bronchus, B. Oesophagus, C. Mid-trachea, D. Left main bronchus', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Right main bronchus", 'role': 'assistant'}]