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: Pharmacology
Which of the following gas exert second gas effect when co-administered with halothane? 
Select and explain. 
A. Nitrous oxide, B. Chloroform, C. Ether, D. Helium
A: Nitrous oxide
Answer: A: Nitrous oxide 
Explanation: Second gas effect, diffusion hypoxia are seen with inhalation agents used in high concentration like nitrous oxide.