This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Skeletal system, Subject name: Radiology
[{'content': 'Fallen fragment sign on X-ray is seen in - \nSelect and explain. \nA. Simple bone cyst, B. Aneurysmal bone cyst, C. GCT, D. Fibrous dysplasia', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Fallen fragment sign and hinged fragment sign are seen in simple bone cyst. Fallen fragment sign refers the settlement of fractured fragment in dependent position Hinged fragment sign (aka Trap door sign) refers to non separation of fractured fragment from the adjacent coex.', 'role': 'assistant'}]