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': 'True about osteoclastoma \nSelect and explain. \nA. Mononuclear cells are malignant component, B. Common in elderly, C. Radiotherapy is the main modality of treatment, D. Diaphyseal lesion', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]