This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Virology, Subject name: Microbiology
The only oncogenic virus whose pathogenicity has been proved without doubt is - 
Select and explain. 
A. HTLV - I, B. HTLV - II, C. HTLV - III, D. HTLV - IV
A: HTLV - I
Answer: A: HTLV - I 
Explanation: HTLV1 present world wide.it causes adult T cell leukemia,tropical dpadtic paraparesid.it mainly infect CD4 cells .infected cell express more inter leukin2 REF:<\p>MICROBIOLOGY ANANTHA NARAYANAN NINTH EDITION PAGE.567