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
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 - 
Select and explain. 
A. Right main bronchus, B. Oesophagus, C. Mid-trachea, D. Left main bronchus
A: Right main bronchus
Answer: A: Right main bronchus 
Explanation: Ans. is 'a' i.e., Right main bronchus