**Core Concept**
Rhabdomyosarcoma is a type of soft tissue sarcoma that arises from skeletal muscle cells. It is the most common type of soft tissue sarcoma in children and adolescents. The disease is characterized by the uncontrolled growth of malignant skeletal muscle cells, leading to the formation of a tumor.

**Why the Correct Answer is Right**
The most common site of rhabdomyosarcoma is the head and neck region, particularly the orbit (eye socket). This is because the head and neck region contains a high concentration of skeletal muscle cells, which are the cells of origin for this type of cancer. The orbit is a common site due to the presence of extraocular muscles, which are rich in skeletal muscle cells. The tumor can grow and invade surrounding tissues, leading to symptoms such as proptosis (bulging of the eye) and vision loss.

**Why Each Wrong Option is Incorrect**
* **Option A:** The genitourinary tract is a less common site for rhabdomyosarcoma, accounting for about 10% of cases.
* **Option B:** The trunk and extremities are also less common sites for rhabdomyosarcoma, accounting for about 20% of cases.
* **Option D:** The abdomen is a rare site for rhabdomyosarcoma, accounting for less than 5% of cases.

**Clinical Pearl / High-Yield Fact**
Rhabdomyosarcoma is a highly malignant tumor that requires prompt treatment, including surgery, chemotherapy, and radiation therapy. Early diagnosis and treatment are crucial for improving outcomes and reducing the risk of metastasis.

**Correct Answer: C. Head and neck region, particularly the orbit.**