This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anesthesia Machine, Subject name: Anaesthesia
[{'content': 'Gas cylinder with single pin index - \nSelect and explain. \nA. Oxygen, B. Air, C. Nitrogen, D. Entonox', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'd' i.e., Entonox GasPin indexOxygen2,5Nitrous oxide3,5Cyclopropane3,6Air1,5Nitrogen1,4Entonox (50% O2 + 50% N2O)Single central (7)Carbon dioxide (< 7[?]5%)2,6Carbon dioxide (>7[?]5%)1,6", 'role': 'assistant'}]