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
During cesarean section under general endotracheal anaesthesia, venous air embolism 
Select and explain. 
A. Is associated with high end-tidal CO2, B. Should be treated with nitrous oxide, C. Is associated with expired nitrogen, D. Induces severe hypertension
C: Is associated with expired nitrogen
Answer: C: Is associated with expired nitrogen 
Explanation: Expired Nitrogen is the most sensitive venous-air embolism detection method, as the largest component of air is nitrogen.