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: Biochemistry
[{'content': 'Generation of free radicals occurs by all of the following mechanisms EXCEPT \nSelect and explain. \nA. Normal metabolism, B. Oxygen toxicity, C. Reperfusion after ischemic injury, D. All of the above', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]