This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Transplantation, Subject name: Surgery
Which of the following is true regarding successful whole- organ pancreas transplantation in type I diabetes? 
Select and explain. 
A. It results in maintenance of normal serum glucose levels, B. Recurrence of diabetic nephropathy in simultaneously transplanted kidneys is not prevented, C. Oral glucose tolerance tests remain abnormal, D. The pathologic changes of diabetic retinopathy are reversed
D: The pathologic changes of diabetic retinopathy are reversed
Answer: D: The pathologic changes of diabetic retinopathy are reversed 
Explanation: Whole-organ pancreas transplantation is the only therapy for type I insulin-dependent diabetes that maintains normal serum glucose levels and normal glucose tolerance tests. When the pancreas is transplanted along with a kidney, the tight glucose control generally prevents the recurrence of diabetic nephropathy. No series has shown the reversal of diabetic retinopathy or reduction in the rate of diabetic ulcers or of amputations, although some parameters of diabetic retinopathy may improve after pancreas transplantation.