An 18-year-old man with a 12-year history of type 1 diabetes mellitus comes to the physician for a follow-up examination. Medications include 25 U of NPH insulin and 10 U of regular insulin in the morning and 10 U of NPH insulin and 10 U of regular insulin before dinner. His hemoglobin A1c was 14.5% 12 weeks ago. His current pulse is 80/min, respirations are 20/min, and blood pressure is 145/95 mm Hg. Examination shows scattered retinal microaneurysms bilaterally. The remainder of the examination shows no other abnormalities. Laboratory studies show:Hemoglobin A1c 13%Serum Na+ 130 mEq/LK+ 3.2 mEq/LCl− 101 mEq/LHCO3− 23 mEq/LGlucose 325 mg/dLCreatinine 1.5 mg/dLCholesterol 350 mg/dLUrineBlood negativeGlucose 4+Protein 1+Ketones negativeWhich of the following is the most likely renal diagnosis?(A) Cholesterol renal emboli(B) Diabetic nephropathy(C) Hypertensive glomerulosclerosis(D) Hypokalemic nephropathy(E) Sodium-losing nephropathy