This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Misc., Subject name: Pathology
Oncogene was first identified in 
Select and explain. 
A. Epstein-Barr Virus, B. Echovirus, C. Adenovirus, D. Retrovirus
D: Retrovirus
Answer: D: Retrovirus 
Explanation: (D) Retrovirus > Cellular Protooncogenes were first discovered in their mutated or "oncogenic" forms as "passengers" within the genome of acute transforming retroviruses by the 1989 Nobel laureates Harold Varmus and Michael Bishop.