## Core Concept
The Glomerular Filtration Rate (GFR) is a key indicator of kidney function, representing the volume of fluid filtered from the renal (kidney) glomerular capillaries into the Bowman's capsule per unit time. In a normal adult, GFR is used to assess the kidney's ability to filter waste and excess fluids from the blood.

## Why the Correct Answer is Right
The correct GFR value for a normal adult is approximately **120 mL/min/1.73m²**. This value can vary slightly based on factors such as age, sex, and body size, but 120 mL/min/1.73m² is a widely accepted reference range. The GFR is often estimated using the Modification of Diet in Renal Disease (MDRD) equation or the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, which take into account serum creatinine levels, age, sex, and race.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not provide a specific value that aligns with the known normal range for GFR.
- **Option B:** Similarly, this option lacks a specific value but is presumably incorrect based on the same reasoning.
- **Option D:** This option suggests a value that is significantly lower than the accepted normal range for GFR in a healthy adult.

## Clinical Pearl / High-Yield Fact
A crucial point to remember is that GFR **naturally declines with age**. By the age of 40, the GFR may decrease by about 1 mL/min/1.73m² per year. This decline can be accelerated by conditions such as diabetes, hypertension, and chronic kidney disease. Therefore, it's essential to consider age when interpreting GFR values.

## Correct Answer: C. 120 mL/min/1.73m².