**Core Concept**
Simple bone cyst, also known as unicameral bone cyst, is a benign bone lesion that typically affects the metaphysis of long bones in children and adolescents. It is characterized by an expansile lytic lesion with a thin cortical shell, often causing pain and swelling.

**Why the Correct Answer is Right**
Simple bone cysts are most commonly found in the humerus and femur, with a predilection for the upper third of the humerus. The expansile nature of the lesion is due to the accumulation of fluid within the cyst, which can cause thinning of the cortical shell and lead to pain and swelling. The diagnosis is often supported by radiographic findings, including an expansile lytic lesion with a well-defined margin and a thin cortical shell.

**Why Each Wrong Option is Incorrect**
**Option A:** Aneurysmal bone cyst is a type of benign bone lesion, but it typically has a more aggressive appearance on radiographs, with multiple fluid-filled cavities and a thicker cortical shell.

**Option C:** Giant cell tumor is a type of benign bone tumor that typically affects the epiphysis of long bones in adults, rather than the metaphysis of children.

**Option D:** Osteosarcoma is a type of malignant bone tumor that is characterized by aggressive radiographic features, including cortical destruction and periosteal reaction, which is not seen in simple bone cysts.

**Clinical Pearl / High-Yield Fact**
The "honeycomb" appearance on radiographs, due to the presence of multiple small cysts within the bone, is a characteristic feature of aneurysmal bone cyst, but not simple bone cyst.

**✓ Correct Answer: B. Simple bone cyst**