**Core Concept**
The underlying principle being tested is the identification of a specific type of ovarian tumor based on its gross appearance. Ovarian tumors can be benign or malignant and vary in their histological characteristics.

**Why the Correct Answer is Right**
Given the age of the patient and the description of the mass, the most likely diagnosis is a **germ cell tumor**, specifically a **dermoid cyst** (mature cystic teratoma). These tumors are common in young women and can present as a palpable abdominal mass. They are benign and contain elements from all three germ layers.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because it does not match the typical presentation of a dermoid cyst.
**Option B:** This option is also incorrect as it is not consistent with the clinical scenario provided.
**Option C:** Similarly, this choice does not align with the expected findings for the described condition.
**Option D:** This option is incorrect as it is not the most probable diagnosis based on the given clinical context.

**Clinical Pearl / High-Yield Fact**
Dermoid cysts are a type of germ cell tumor that can contain hair, teeth, and other tissue types. They are usually benign but can become complicated by torsion or rupture.

**Correct Answer: D. Dermoid Cyst**