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: Orthopaedics
[{'content': "A 20 year old young patient has sclerotic lesion at diaphysis, most likely diagnosis \nSelect and explain. \nA. Osteosarcoma, B. Ewing's sarcoma, C. Osteoid osteoma, D. Osteochondroma", 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]