## Core Concept
The core concept being tested here is the metabolic adaptation of neurons during starvation. Neurons have specific fuel preferences under different conditions, and understanding these preferences is crucial for managing various clinical scenarios.

## Why the Correct Answer is Right
During starvation, the body's primary source of energy, glucose, becomes depleted. The brain, which is highly dependent on glucose under normal conditions, must adapt to utilize alternative fuel sources. **Ketone bodies**, produced by the liver from fatty acids, become a critical energy source for the brain during prolonged fasting or starvation. This adaptation allows the brain to function while conserving muscle mass. The correct answer, **ketone bodies**, is right because neurons can indeed use ketone bodies as an alternative fuel during starvation.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because, although glucose is the primary fuel for neurons under normal conditions, the question specifically asks about the fuel used during starvation when glucose levels are low.
- **Option B:** This option is incorrect because while fatty acids are a crucial energy source for many tissues during starvation, neurons cannot directly use fatty acids due to the blood-brain barrier and the lack of necessary enzymes for fatty acid metabolism within neurons.
- **Option C:** This option might seem plausible but is incorrect because it does not accurately represent the primary alternative fuel source that neurons switch to during starvation.

## Clinical Pearl / High-Yield Fact
A critical clinical pearl is that the brain's adaptation to use **ketone bodies** during starvation is a protective mechanism that reduces the brain's dependence on glucose, thereby helping to preserve muscle mass and prolong survival during periods of famine or when food is scarce.

## Correct Answer Line
**Correct Answer: D. ketone bodies**