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': 'In normal anaesthesia fresh minimum gas flows O2 delivery – \nSelect and explain. \nA. 21%, B. 33%, C. 51%, D. 75%', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Anaesthesia is maintained with a controlled mixture of oxygen (minimum 33%) + nitrous oxide (66%) + inhalational agent (most commonly halothane).', 'role': 'assistant'}]