Step 1: Understanding the question.
The question asks for the leading cause of CKD in adults, which is often linked to metabolic disorders.
Step 2: Analyzing the options.
(A) Diabetic nephropathy: Correct — Diabetes is the most common cause globally.
(B) Hypertensive nephropathy: Second most common.
(C) Glomerulonephritis: More common in developing countries but not the top.
(D) Polycystic kidney disease: Genetic and less prevalent.
Step 3: Conclusion.
The correct answer is (A) Diabetic nephropathy, as it is the most common cause of chronic kidney disease.