All are the predisposing factors of osteogenic sarcoma except -: (A) Paget's disease of bone, (B) Radiation, (C) Viral infection, (D) Bone infarction
Answer is C. Causes of secondary osteosarcoma : 

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