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': 'High air flow oxygen enriched devices \nSelect and explain. \nA. Are variable performance devices, B. Deliver constant concentrations of oxygen, C. Require oxygen entrainment, D. Require closed face masks.', 'role': 'user'}, {'content': 'Answer: B \nExplanation: High air flow oxygen enriched devices are fixed performance devices and deliver constant concentration of oxygen. They require face masks with holes to enable high volumes of air to entrained.', 'role': 'assistant'}]