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
Most serious complication of paget's disease is: 
Select and explain. 
A. Osteosarcoma., B. Osteoma., C. Ewing sarcoma., D. All of the above.
A: Osteosarcoma.
Answer: A: Osteosarcoma. 
Explanation: Development of osteosarcoma is the most serious complication of paget's disease or osteitis deformans.