## Core Concept
The question pertains to the regulation of glycogen metabolism, specifically focusing on an enzyme in the liver that is converted from an inactive dephosphorylated state to an active phosphorylated state. This process is crucial for the mobilization of glycogen stores in response to energy demands.

## Why the Correct Answer is Right
The enzyme in question is **glycogen phosphorylase**. In its inactive, dephosphorylated form, glycogen phosphorylase is known as glycogen phosphorylase b. When phosphorylated, it becomes the active form, glycogen phosphorylase a. This conversion is catalyzed by **phosphorylase kinase**, which adds a phosphate group to glycogen phosphorylase b, activating it. The active form of glycogen phosphorylase is essential for breaking down glycogen into glucose-1-phosphate, which can then be converted into glucose-6-phosphate for use in glycolysis or, in the liver, converted into glucose for release into the bloodstream.

## Why Each Wrong Option is Incorrect
- **Option A:** Without specific details on the options provided, we can infer that any option suggesting an incorrect mechanism, enzyme, or outcome related to the activation of glycogen phosphorylase would be incorrect. For instance, if an option suggested that the dephosphorylated form was active or that a different enzyme was involved in this specific step, it would be incorrect.
- **Option B:** Similarly, any option that inaccurately describes the role, regulation, or form of glycogen phosphorylase would be incorrect. This could include misidentifying the enzyme, its activators, or its role in glycogen metabolism.
- **Option C:** This option would be incorrect if it proposed an alternative that did not align with the established biochemical pathway of glycogen phosphorylase activation.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **glycogen storage diseases**, such as von Gierke's disease (Type I), Cori's disease (Type III), and McArdle's disease (Type V), are related to defects in glycogen metabolism. Understanding the regulation and activity of enzymes like glycogen phosphorylase is crucial for comprehending these diseases. For example, McArdle's disease is characterized by a deficiency in myophosphorylase, the muscle isoform of glycogen phosphorylase.

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