This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anaesthetic equipments, Subject name: Anaesthesia
[{'content': 'In hyperbaric oxygenation the maximum allowed pressure of O2 is \nSelect and explain. \nA. 3 atm, B. 1 atm, C. 5 atm, D. 9 atm', 'role': 'user'}, {'content': 'Answer: A \nExplanation: At 3 atm, an aerial oxygenation of nearly 2200 mm Hg may be achieved .', 'role': 'assistant'}]