**Core Concept**
Granulosa cell tumors are a type of sex cord-stromal tumor that arises from the ovarian stroma, specifically from the granulosa cells. These tumors are known for their potential to produce estrogen, leading to precocious puberty in young girls.

**Why the Correct Answer is Right**
The characteristic histologic finding of granulosa cell tumors is the presence of **Call-Exner bodies**. These are small, round, or ovoid structures composed of a central rosette of granulosa cells surrounded by a basement membrane and often a halo of eosinophilic material. The presence of Call-Exner bodies is a diagnostic hallmark of granulosa cell tumors. The estrogen produced by these tumors can lead to precocious puberty, as seen in this 5-year-old girl.

**Why Each Wrong Option is Incorrect**
**Option A:** The presence of **Hilus cells** is a characteristic feature of Sertoli-Leydig cell tumors, not granulosa cell tumors.
**Option B:** **Fibrosarcoma** is a type of malignant tumor that arises from fibroblasts, and it is not associated with granulosa cell tumors.
**Option C:** **Theca cell tumors** are a type of sex cord-stromal tumor, but they are not characterized by Call-Exner bodies.

**Clinical Pearl / High-Yield Fact**
Granulosa cell tumors can produce estrogen, leading to precocious puberty in young girls. A high index of suspicion should be maintained for these tumors in cases of precocious puberty, especially in the presence of an ovarian mass.

**Correct Answer:** C. Call-Exner bodies.