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': "X-ray appearance of osteosarcoma are all except- \nSelect and explain. \nA. Periosteal reaction, B. Codman's triangle, C. Soap-bubble, D. Sunray appearance", 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]