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
[{'content': "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: \nSelect and explain. \nA. Osteosarcoma, B. Ewing's sarcoma, C. Osteoclastoma, D. Chondroblastoma", 'role': 'user'}, {'content': "Answer: A \nExplanation: 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.", 'role': 'assistant'}]