**Core Concept**
Cementum is a thin layer of bone-like tissue covering the root of a tooth, playing a crucial role in tooth anchorage and sensation. It is rich in collagen fibers and hydroxyapatite crystals, which provide its unique properties.

**Why the Correct Answer is Right**
Cementum is avascular, meaning it lacks blood vessels. This characteristic is essential for its function as a thin, non-bony layer that covers the root of the tooth. The avascularity of cementum is due to the absence of a rich vascular supply, which allows it to maintain its mineralized structure and provide a smooth surface for the attachment of the periodontal ligament fibers.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided, so we cannot evaluate its correctness.
* **Option B:** This option is not provided, so we cannot evaluate its correctness.
* **Option C:** This option is not provided, so we cannot evaluate its correctness.

**Clinical Pearl / High-Yield Fact**
It is essential to note that cementum is not a bony tissue, despite its composition and function. This distinction is critical in dental and oral surgery, as cementum has different properties and requirements compared to bone.

**Correct Answer:** D.