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: Physiology
Aging is most probably due to: 
Select and explain. 
A. Non random mutation in somatic cells, B. Decrease in collagen cross linkage, C. Increase in superoxidase dismutase, D. Accumulated free radical injury in tissue
D: Accumulated free radical injury in tissue
Answer: D: Accumulated free radical injury in tissue 
Explanation: Accumulated free radical injury in tissue