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': 'Safety pin index for oxygen cylinder is \nSelect and explain. \nA. 3,5, B. 1,5, C. 2,5, D. 1,4', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]