**Core Concept**
The underlying principle being tested is the regulation of glycogen metabolism, specifically the control of glycogen phosphorylase, an enzyme crucial for the breakdown of glycogen into glucose-1-phosphate. This process is vital in the liver and muscles for energy production. The enzyme exists in two forms: phosphorylase a (active) and phosphorylase b (less active).

**Why the Correct Answer is Right**
Phosphorylase b is maintained in an inactivated state by the absence of phosphorylation. Normally, phosphorylase b kinase phosphorylates and activates phosphorylase b, converting it into its active form, phosphorylase a. This activation is part of the body's mechanism to mobilize glucose stores during stress or low blood glucose levels.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it doesn't directly relate to the maintenance of phosphorylase b in an inactivated state.
**Option B:** Incorrect as it is not the primary mechanism by which phosphorylase b is kept inactivated.
**Option C:** Incorrect because because it is not directly involved in the inactivation of phosphorylase b.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the regulation of glycogen metabolism involves a complex interplay of enzymes and signaling pathways, including the activation of phosphorylase b to phosphorylase a, which is crucial for the rapid mobilization of glucose.

**Correct Answer:** D. Phosphorylase b kinase in an inactive state or the absence of its activity maintains phosphorylase b in an inactivated state.