**Core Concept**
The question is testing the understanding of the principles of **retention and resistance** in cast restorations, which are crucial for the longevity and success of the restoration. The design of a cast restoration, including the walls and margins, plays a significant role in its retention and resistance to occlusal forces.

**Why the Correct Answer is Right**
A long and less divergent wall in a cast restoration increases the **surface area** in contact with the tooth, enhancing the **frictional retention**. Less divergence means the walls are more parallel, which improves the resistance form by distributing the occlusal forces more evenly throughout the restoration, thereby reducing the likelihood of dislodgement or fracture.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while important, it doesn't directly relate to the specific design feature mentioned.
**Option B:** Incorrect as it is not the primary benefit of less divergent walls.
**Option C:** Incorrect because increased divergence, not less, would lead to decreased retention due to less surface contact.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the design of a cast restoration, including the length and divergence of its walls, significantly impacts its retention and resistance to failure. Proper design can prevent complications such as restoration fracture or dislodgement.

**Correct Answer:** D. Increased retention and resistance.