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: Radiology
[{'content': "Which of the following malignant tumours is radioresistant? \nSelect and explain. \nA. Ewing's sarcoma, B. Retinoblastoma, C. Osteosarcoma, D. Osteosarcoma", 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. Osteosarcoma', 'role': 'assistant'}]