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': 'All of the following are used to maintain proper oxygen flow to the patient except – \nSelect and explain. \nA. Placement of Oxygen flowmeter downstream of the Nitrogen flowmeter, B. A proportionater between N2 and O2 control valve, C. Different pin index for nitrogen and oxygen, D. Calibrated oxygen concentration analyses', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Pin index safety system for cylinders is to prevent incorrect cylinder attachment (not to prevent hypoxia).', 'role': 'assistant'}]