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: Medicine
The greatest degree of association with the severity of diabetic nephropathy in a 30-year-old diabetic is which of the following? 
Select and explain. 
A. Duration of disease, B. Type of disease, C. Retinal involvement, D. None of the above
A: Duration of disease
Answer: A: Duration of disease 
Explanation: Duration of the illness contibuted to the severity and poor prognosis.