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': 'Laughing gas is: March 2005 \nSelect and explain. \nA. Ketamine, B. Nitric oxide, C. Nitrous oxide, D. Methane', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. C: Nitrous oxide Nitrous oxide is known as "laughing gas" due to the euphoric effects of inhaling it, a propey that has led to its recreational use as a dissociative hallucinogen', 'role': 'assistant'}]