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: Orthopaedics
All are the predisposing factors of osteogenic sarcoma except - 
Select and explain. 
A. Paget's disease of bone, B. Radiation, C. Viral infection, D. Bone infarction
C: Viral infection
Answer: C: Viral infection 
Explanation: Causes of secondary osteosarcoma : 

Paget disease 
Fibrous dysplasia
Multiple osteochondroma
Chronic osteomyelitis
Radiation  
Enchondromatosis  
Bone infarction