**Core Concept**
The question tests understanding of renal physiology, specifically the reabsorption of substances in the nephron. **Tubular reabsorption** is the process by which the kidney reclaims useful substances from the filtrate back into the bloodstream.

**Why the Correct Answer is Right**
Without the specific options provided, the general concept of least reabsorption can be applied to substances like **creatinine**, which is poorly reabsorbed by the renal tubules. The amount of reabsorption varies among different substances, with some like **glucose** and **amino acids** being almost completely reabsorbed under normal conditions, while others like **water** and **electrolytes** have variable reabsorption rates depending on the body's needs.

**Why Each Wrong Option is Incorrect**
**Option A:** Without specifics, we can't directly address why each option is incorrect, but generally, substances with high reabsorption rates, like glucose, would be incorrect if we're looking for the least reabsorption.
**Option B:** Similarly, if this option represents a substance with significant reabsorption, it would not be the correct answer.
**Option C:** This could potentially represent a substance with low reabsorption, but without specifics, it's hard to determine its correctness.
**Option D:** If this option has a higher reabsorption rate than the correct answer, it would be incorrect.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the kidney's ability to reabsorb or secrete substances is crucial for maintaining **electrolyte balance** and **acid-base balance**. Understanding which substances are reabsorbed or secreted to what extent is vital for managing renal and electrolyte disorders.

**Correct Answer:** Correct Answer: D. Creatinine.