This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
15 year old boy presented with a mass in the distal femur. X-ray from the lesion showed features of Codman's triangle and Sunray appearance. The diagnosis is: 
Select and explain. 
A. Osteosarcoma, B. Ewing's sarcoma, C. Osteoclastoma, D. Chondroblastoma
A: Osteosarcoma
Answer: A: Osteosarcoma 
Explanation: Codman's triangle and Sunray appearance are characteristic radiological findings in osteosarcoma. When the tumour elevates the periosteum of bone, a gap occurs between periosteum and bone, where the gap is elevated, bone is formed, creating a triangular shape on radiographs. Ref: Apley's system of ohopaedics and fractures;8th/185; Essential ohopedics by Maheshwari 3rd/219, 222.