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: Pathology
[{'content': "Most serious complication of paget's disease is: \nSelect and explain. \nA. Osteosarcoma., B. Osteoma., C. Ewing sarcoma., D. All of the above.", 'role': 'user'}, {'content': "Answer: A \nExplanation: Development of osteosarcoma is the most serious complication of paget's disease or osteitis deformans.", 'role': 'assistant'}]