**Core Concept**
Ewing's sarcoma is a malignant bone tumor characterized by a specific genetic translocation involving the EWS gene, leading to the formation of an abnormal EWS-FLI1 fusion protein. This fusion protein disrupts normal transcriptional regulation, contributing to the development and progression of the tumor.

**Why the Correct Answer is Right**
The most common site of Ewing's sarcoma is the diaphysis (shaft) of long bones, particularly in the pelvis, femur, tibia, and humerus. This is due to the high concentration of osteoblasts and osteoclasts in these areas, which are susceptible to the malignant transformation caused by the EWS-FLI1 fusion protein. The tumor often presents with a "moth-eaten" appearance on radiographs, due to the lytic lesions and periosteal reaction characteristic of this disease.

**Why Each Wrong Option is Incorrect**
**Option A:** The metaphysis (growth plate) of long bones is a common site for osteosarcoma, not Ewing's sarcoma.
**Option B:** The vertebral bodies are more commonly affected by osteosarcoma and chordoma, not Ewing's sarcoma.
**Option C:** The ribs are not a typical location for Ewing's sarcoma, which more commonly affects the long bones and pelvis.

**Clinical Pearl / High-Yield Fact**
Ewing's sarcoma is the second most common primary bone malignancy in children and adolescents, after osteosarcoma. It often presents with systemic symptoms such as fever, weight loss, and fatigue, in addition to local symptoms like pain and swelling at the tumor site.

**Correct Answer:** C. Pelvis and long bones, particularly the femur, tibia, and humerus.