This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ohopedics Oncology, Subject name: Orthopaedics
[{'content': "Epiphyseal tumor before fusion of epiphysis: \nSelect and explain. \nA. Chondroblastoma, B. Chondrosarcoma, C. Ewing's sarcoma, D. Giant cell tumor", 'role': 'user'}, {'content': "Answer: A \nExplanation: MOST COMMON SITE OF PRIMARY BONE TUMORS (Epiphyseal) Chondroblastoma (before physeal closure)-purely epiphyseal Osteoclastoma/Giant cell tumor (after physeal closure in adults). Aicular osteochondroma. Clear cell chondrosarcoma. Ewing's Sarcoma : is diaphyseal(middle of the shaft) Chondrosarcoma: Occurs in bones formed with endosteal formation e.g.proximal femur, pelvis, proximal humerus, distal femur, scapula Usually metaphyseal.", 'role': 'assistant'}]