The correct answer is: "both renal cortex and renal medulla."
Explanation:
1. Nephrons, which are the functional units of the kidney responsible for filtering the blood and producing urine, are found in both the renal cortex and renal medulla.
2. The renal cortex is the outer portion of the kidney where the initial processes of filtration and urine formation begin.
3. The renal medulla is the inner part of the kidney where further concentration and modification of urine occur as part of the nephron's function.
4. Therefore, nephrons are distributed throughout both the renal cortex and renal medulla to carry out their vital functions in the process of urine formation and waste excretion.
