**Core Concept**
The counter bevel is an essential feature in cast restorations, particularly in inlays, onlays, and crowns. It is designed to reduce stress concentrations and improve the marginal seal of the restoration. The angulation of the counter bevel is critical in achieving optimal results.

**Why the Correct Answer is Right**
The correct answer is determined by the need to minimize the likelihood of the restoration's marginal gap being compromised by the bevel. A counter bevel that is angled too aggressively can lead to an increased risk of marginal leakage and restoration failure. The optimal angulation is typically between 10° and 20°, allowing for adequate removal of the tooth structure while maintaining the integrity of the marginal seal. This is achieved by taking into account the anatomy of the tooth, the type of restoration, and the material being used.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because an angle of 30° or greater would be too aggressive, leading to excessive removal of tooth structure and increased risk of marginal leakage.
**Option B:** Incorrect because an angle of 5° or less would be insufficient, potentially leaving behind a rough surface and compromising the marginal seal.
**Option C:** Incorrect because an angle of 45° would be excessive, leading to an increased risk of marginal leakage and restoration failure.

**Clinical Pearl / High-Yield Fact**
The angulation of the counter bevel should be carefully planned and executed to ensure optimal results. A general rule of thumb is to use a bevel angle of 10° to 20° for most cast restorations, with adjustments made based on the specific needs of the case.

**Correct Answer:** D.