## Core Concept
Ketone bodies are molecules (acetoacetate, β-hydroxybutyrate, and acetone) produced by the liver from fatty acids during periods of low food intake, carbohydrate restrictive diets, prolonged intense exercise, or in uncontrolled type 1 diabetes. They serve as an alternative energy source for various tissues, especially the brain, which cannot use fatty acids directly for energy.

## Why the Correct Answer is Right
The correct answer involves the conversion of ketone bodies into a form that can be utilized by tissues for energy. This process primarily occurs in the liver and other tissues. **Acetoacetate** is converted into **β-hydroxybutyrate** and acetone. However, for utilization, **β-hydroxybutyrate** is converted back into acetoacetate by **β-hydroxybutyrate dehydrogenase** in the mitochondria of tissues. Acetoacetate is then activated to **acetoacetyl-CoA** by **acetoacetyl-CoA thiolase** and further into **two molecules of acetyl-CoA** by **acetoacetyl-CoA thiolase** and **HMG-CoA synthase** is not directly involved but **HMG-CoA** is an intermediate in ketone body synthesis. Acetyl-CoA can then enter the citric acid cycle for energy production.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not accurately represent a step in the utilization of ketone bodies.
- **Option B:** This option is incorrect because, although HMG-CoA is involved in the synthesis of ketone bodies, it is not directly involved in their utilization.
- **Option D:** This option is incorrect because it inaccurately suggests a direct conversion that is not relevant to the utilization pathway of ketone bodies.

## Clinical Pearl / High-Yield Fact
A key clinical point is that during fasting or starvation, the brain adapts to use ketone bodies as a significant energy source, reducing its dependence on glucose. This adaptation is crucial for survival during periods of nutrient scarcity.

## Correct Answer Line
**Correct Answer: C.**