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
What is the sequence which a retrovirus follows on entering a host cell - 
Select and explain. 
A. RNA-DNA-RNA, B. RNA-DNA, C. DNA-RNA, D. DNA-RNA-DNA
A: RNA-DNA-RNA
Answer: A: RNA-DNA-RNA 
Explanation: when virus infect a cell viral RNA is transcribed by enzyme first into ssDNA then to dsDNA REF:MICROBIOLOGY ANANTHA NARAYANAN NINTH EDITION PAGE.571