**Core Concept**
The question is testing the knowledge of the most common tumor of the eyelid, which involves identifying the prevalence and characteristics of various eyelid tumors.

**Why the Correct Answer is Right**
The most common tumor of the eyelid is the **Basal Cell Carcinoma (BCC)**. BCC arises from the basal cells of the epidermis and is often associated with sun exposure. It tends to grow slowly and locally, but can invade surrounding tissues if left untreated. BCC is more common in areas with high UV radiation, such as the eyelids.

**Why Each Wrong Option is Incorrect**
* **Option A:** Squamous Cell Carcinoma is a common skin cancer, but it is less common than BCC on the eyelid.
* **Option B:** Sebaceous gland carcinoma is a rare but aggressive tumor of the eyelid, and is not the most common type.
* **Option C:** Malignant melanoma is a common skin cancer, but it is relatively rare on the eyelid compared to BCC.

**Clinical Pearl / High-Yield Fact**
It's essential to recognize the appearance of BCC on the eyelid, which often presents as a slowly growing, painless, pearl-like nodule or a pigmented patch.

**Correct Answer:** D. Basal Cell Carcinoma