## **Core Concept**
The renal clearance of a substance is a measure of the volume of plasma from which the substance is completely removed per unit time. It is used to quantify the efficiency of renal excretion. Tubular secretion is a process by which substances are transported from the blood into the renal tubules for excretion.

## **Why the Correct Answer is Right**
The correct answer can be deduced by understanding the concept of renal clearance and its relation to tubular secretion. If a drug's renal clearance exceeds the glomerular filtration rate (GFR), it implies that the drug is not only being filtered at the glomerulus but also being secreted into the renal tubules. The GFR is approximately 120 mL/min in a healthy adult. Therefore, if the renal clearance of drug X is more than 120 mL/min, it indicates that drug X is being secreted through the renal tubules.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Less than 120 mL/min could indicate that the drug is only being filtered at the glomerulus or being reabsorbed, not secreted.
- **Option B:** Equal to 120 mL/min suggests that the drug is being cleared only through glomerular filtration without any additional tubular secretion or reabsorption.
- **Option D:** This option is not provided, but any value less than or equal to GFR would not confirm tubular secretion.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that for a substance to be considered secreted by the renal tubules, its clearance must exceed the GFR. This is a critical concept in pharmacokinetics and renal physiology, helping to understand how drugs are eliminated from the body.

## **Correct Answer:** C. More than 120 mL/min.