**Core Concept**
Codman's triangle is a characteristic radiographic feature of osteosarcoma, formed by the elevation of the periosteum away from the bone cortex, the new bone formation at the edge of the tumor, and the intact periosteum. This phenomenon is due to the aggressive nature of osteosarcoma, which leads to the rapid growth of the tumor, lifting the periosteum and causing new bone formation.

**Why the Correct Answer is Right**
Osteosarcoma is the primary type of sarcoma that displays Codman's triangle due to its highly aggressive nature and the production of osteoid tissue by the tumor cells. The rapid growth of the tumor lifts the periosteum, leading to the formation of a triangle-shaped radiographic feature. This is a key diagnostic feature of osteosarcoma.

**Why Each Wrong Option is Incorrect**
**Option A:** Osteosarcoma - This is the correct answer, and we should not discuss it here.
**Option B:** Ewing's sarcoma - Ewing's sarcoma may show a similar radiographic feature, known as the "onion-skin" appearance, due to the periosteal reaction, but it is not typically associated with Codman's triangle.
**Option C:** Chondrosarcoma - Chondrosarcoma is a type of cartilaginous sarcoma that does not typically display Codman's triangle, as it is a slower-growing tumor that does not cause significant periosteal reaction.
**Option D:** Soft tissue sarcoma - Soft tissue sarcomas do not typically display Codman's triangle, as they do not involve the bone cortex and periosteum to the same extent as osteosarcoma.

**Clinical Pearl / High-Yield Fact**
Remember that Codman's triangle is a key diagnostic feature of osteosarcoma, and its absence or presence should be carefully evaluated in the context of the patient's clinical presentation and radiographic findings.

**Correct Answer: C. Chondrosarcoma. Chondrosarcoma.**