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
[{'content': 'Aging is most probably due to: \nSelect and explain. \nA. Non random mutation in somatic cells, B. Decrease in collagen cross linkage, C. Increase in superoxidase dismutase, D. Accumulated free radical injury in tissue', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Accumulated free radical injury in tissue', 'role': 'assistant'}]