## Core Concept
The kidneys receive a significant portion of the cardiac output, which is essential for their function in filtering waste and excess fluids from the blood. This high blood flow is necessary for the kidneys to perform their critical role in maintaining electrolyte balance, regulating blood pressure, and ensuring proper fluid status.

## Why the Correct Answer is Right
The correct answer, , indicates that approximately 20% of the cardiac output flows through the kidneys. Given that the average cardiac output is about 5 liters per minute (L/min) at rest, this translates to roughly 1 L/min of blood flow through both kidneys. This high rate of blood flow is crucial for the glomerular filtration process, where a significant amount of fluid is filtered out of the blood and into the nephrons for urine production.

## Why Each Wrong Option is Incorrect
* **Option A:** This option suggests a much lower percentage of cardiac output, which would not support the necessary level of glomerular filtration for effective kidney function.
* **Option B:** This option implies a slightly lower than accurate share, which still underestimates the significant proportion of cardiac output dedicated to renal perfusion.
* **Option D:** This option indicates a much higher percentage than is physiologically accurate, suggesting an unrealistic allocation of cardiac output to the kidneys.

## Clinical Pearl / High-Yield Fact
A key point to remember is that despite the kidneys constituting only about 1% of the total body weight, they receive 20% of the cardiac output. This highlights the critical role of the kidneys in overall cardiovascular and metabolic homeostasis. A classic clinical correlation is that a decrease in renal blood flow can rapidly lead to acute kidney injury (AKI) or exacerbate chronic kidney disease (CKD).

**Correct Answer: C. **