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: Anaesthesia
[{'content': 'Standard method to differentiate between endotracheal and esophageal intubation is? \nSelect and explain. \nA. End tidal CO2, B. Chest X-rays, C. Auscultation, D. Paial pressure of 02', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., End tidal CO2", 'role': 'assistant'}]