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': 'Bone within bone appearance is seen in – \nSelect and explain. \nA. CML, B. Osteoporosis, C. Osteopetrosis, D. Bone infarct', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Bone within a bone appearance may be seen in osteopetrosis.', 'role': 'assistant'}]