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: Surgery
[{'content': 'The beneficial effect of oxygen therapy in histotoxic\nhypoxia is about \nSelect and explain. \nA. 0%, B. 50%, C. 100%, D. 30%', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]