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: Medicine
[{'content': "Chang staging is used for - \nSelect and explain. \nA. Retinoblastoma, B. Medulloblastoma, C. Ewing's sarcoma, D. Rhabdomyosarcoma", 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]