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
Generation of free radicals occurs by all of the following mechanisms EXCEPT 
Select and explain. 
A. Normal metabolism, B. Oxygen toxicity, C. Reperfusion after ischemic injury, D. All of the above
C: Reperfusion after ischemic injury
Answer: C: Reperfusion after ischemic injury 
Explanation: None