<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:An 81-year-old man presents to his primary care physician for his yearly exam. His past medical history is significant for osteopenia, nephrolithiasis, and hypertension. His family history is significant for relatives who had early onset kidney failure. He takes occasional acetaminophen and supplemental calciumvitamin D. He is physically active with a normal body mass index BMI and has no current concerns. Review of his laboratory results today were compared with those from 15 years ago with the following findings:Results today:Serum creatinine concentration: 1.1 mgdLUrine creatinine concentration: 100 mgdLUrine volume: 1000 mLdayResults 15 years ago:Serum creatinine concentration: 1.1 mgdLUrine creatinine concentration: 120 mgdLUrine volume: 1000 mLdayWhich is the most likely cause of these changes in his creatinine clearance?? A: Benign prostatic hyperplasia, B: Nephrolithiasis, C: Normal aging, D: Polycystic kidney disease, E: Renovascular disease,  <response>: This is a question about interpreting changes in a patients kidney function over time based on serum creatinine, urine creatinine, and urine volume. The key findings are that the patients serum creatinine is unchanged, but his urine creatinine has decreased over 15 years. This indicates that his creatinine clearance has decreased, even though his serum creatinine is stable. The answer choices list various kidney and urinary tract conditions. We can rule out choices related to specific diseases like polycystic kidney disease or renovascular disease, since there is no indication the patient has these. Nephrolithiasis is in his history, but there is no link to the lab value changes. Benign prostatic hyperplasia can cause urinary obstruction but would not explain the decreased creatinine clearance. Therefore, the most likely explanation is normal aging, which commonly leads to gradually decreased kidney function over time. This fits with the patients age of 81 years old.C: Normal aging 