**Core Concept**
The patient's presentation with primary infertility and a palpable pelvic mass, along with elevated CA-125 levels, suggests a gynecological malignancy. This scenario requires consideration of various ovarian tumors, including epithelial ovarian cancer, which is the most common type of ovarian malignancy in women of reproductive age.

**Why the Correct Answer is Right**
The patient's symptoms and elevated CA-125 levels are consistent with epithelial ovarian cancer. CA-125 is a tumor marker commonly elevated in epithelial ovarian cancer, particularly in serous and mucinous subtypes. The presence of a palpable pelvic mass supports this diagnosis, as ovarian tumors can cause abdominal distension and palpable masses. The patient's primary infertility may also be related to the underlying ovarian pathology.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not address the patient's presentation with a palpable pelvic mass and elevated CA-125 levels. Ovarian torsion is a surgical emergency, but it does not account for the patient's chronic symptoms and elevated tumor marker.

**Option B:** This option is incorrect as it is a benign condition that does not typically present with a palpable pelvic mass or significantly elevated CA-125 levels. Ovarian cysts are common in women of reproductive age, but they usually regress spontaneously or are asymptomatic.

**Option C:** This option is incorrect as it is a type of ovarian tumor, but it is not the most common type in women of reproductive age. Theca cell tumors are typically associated with hormonal abnormalities, such as precocious puberty or virilization, rather than primary infertility and a palpable pelvic mass.

**Clinical Pearl / High-Yield Fact**
In the evaluation of a patient with a palpable pelvic mass and elevated CA-125 levels, it is essential to consider the possibility of epithelial ovarian cancer, particularly in women of reproductive age with primary infertility.

**Correct Answer:** C.