**Core Concept**
Prerenal azotemia (PRA) and Acute Tubular Necrosis (ATN) are two common causes of acute kidney injury (AKI). While PRA is characterized by a decrease in renal blood flow leading to a decrease in glomerular filtration rate (GFR), ATN involves direct damage to the renal tubules resulting in a loss of functional nephrons.

**Why the Correct Answer is Right**
The key differentiating feature between PRA and ATN is the presence of a high fractional excretion of sodium (FeNa) in ATN. In ATN, the renal tubules are damaged, leading to an inability to reabsorb sodium, resulting in a high FeNa (>3%). On the other hand, in PRA, the renal blood flow is decreased, leading to an increased reabsorption of sodium, resulting in a low FeNa (3%) in the setting of AKI is highly suggestive of ATN, while a low FeNa (<1%) is more indicative of PRA. However, it's essential to consider the clinical context and other laboratory findings to make an accurate diagnosis. **Correct Answer: C.**