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': '46 yr old chronic smoker came to emergency dept with a history of difficulty in breathing & fever since 1day, postgraduate tells you to connect face mask to which pin index number \nSelect and explain. \nA. 1, 5, B. 2, 5, C. 3, 5, D. 1, 6', 'role': 'user'}, {'content': 'Answer: B \nExplanation: - Machines are usually equipped with one or two E type cylinders that hang on specific hanger yokes. - The medical gas pin-index safety system ensures that the correct medical gas cylinder is hung in the correct yoke. Gas Index Pins Oxygen 2,5 Nitrous oxide 3,5 Cyclopropane 3,6 O2-CO2 (CO2<7.5%) 2,6 O2-CO2(CO2>7.5%) 1,6 O2-he(He>80.5%) 4,6 O2-he(He<80.5%) 2,4 Air 1,5 Nitrogen 1,4 N2O-O 7', 'role': 'assistant'}]