## Core Concept
The question tests knowledge of enzyme regulation, specifically focusing on the activity states of certain enzymes in relation to their phosphorylation status. In biochemical pathways, enzymes can be activated or inhibited through phosphorylation or dephosphorylation, which is a critical regulatory mechanism.

## Why the Correct Answer is Right
The correct answer, **D. Protein kinase B (Akt)**, is active in its dephosphorylated state to some extent but full activation typically requires phosphorylation. However, among the given options and common knowledge, **Glycogen synthase** and **Phosphorylase kinase** are well-known examples where the activity is regulated by phosphorylation status but in a manner opposite to the question's requirement. **Protein phosphatase 2B (Calcineurin)** is indeed active in its dephosphorylated state. Calcineurin is a calcium/calmodulin-dependent serine/threonine phosphatase that plays a critical role in signaling pathways. It is noteworthy for its role in T-cell activation.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is blank and cannot be evaluated.
- **Option B:** This option is also blank and cannot be assessed.
- **Option C:** Similarly, this option is blank and does not provide information for evaluation.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **Calcineurin** (or **Protein phosphatase 2B**) is crucial in the context of immunosuppression. Drugs like cyclosporin A and tacrolimus inhibit calcineurin, thereby suppressing the immune response. This is a high-yield fact for exams, especially when considering mechanisms of action of immunosuppressive drugs.

## Correct Answer Line
**Correct Answer: D. Protein phosphatase 2B (Calcineurin).**