## Core Concept
The "onion-peel" appearance is a radiological finding typically associated with certain bone lesions. This characteristic appearance is due to layers of reactive bone formation around a lesion, resembling the layers of an onion. It is a feature often seen in specific types of bone tumors or lesions.

## Why the Correct Answer is Right
The correct answer, **C. Ewing's Sarcoma**, is associated with an "onion-peel" appearance due to the characteristic layered or laminated periosteal reaction. Ewing's Sarcoma is a malignant bone tumor that often presents in children and adolescents. The tumor's rapid growth leads to the elevation of the periosteum, and as the periosteum tries to form new bone in response, it creates layers of bone, resulting in the "onion-peel" appearance on radiographs.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because, although osteosarcoma can exhibit a variety of radiographic features, the "onion-peel" appearance is not typically characteristic of this tumor. Osteosarcoma more commonly shows a "sunburst" pattern due to direct bone formation within the tumor.
- **Option B:** This option is incorrect as the "onion-peel" appearance is not a hallmark of this condition.
- **Option D:** This option is incorrect because the "onion-peel" appearance is specifically associated with Ewing's Sarcoma, not with this condition.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that when you encounter a bone lesion with an "onion-peel" appearance on radiographs, Ewing's Sarcoma should be highly considered in the differential diagnosis, particularly in pediatric and adolescent patients. This radiographic feature, combined with clinical presentation and histopathological examination, aids in the definitive diagnosis.

**Correct Answer: C. Ewing's Sarcoma**