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
Standard method to differentiate between endotracheal and esophageal intubation is? 
Select and explain. 
A. End tidal CO2, B. Chest X-rays, C. Auscultation, D. Paial pressure of 02
A: End tidal CO2
Answer: A: End tidal CO2 
Explanation: Ans. is 'a' i.e., End tidal CO2