Which one of the following is a retrovirus?

Explanation

HIV is a retrovirus because it contains RNA as its genome and uses the enzyme reverse transcriptase to convert this RNA into DNA, which then integrates into the host cell's genome. This unique replication strategy (RNA → DNA → RNA → protein) is the defining feature of retroviruses. In contrast, both the mumps virus (Paramyxoviridae) and the influenza virus (Orthomyxoviridae) are RNA viruses that do not use reverse transcription. They carry negative-sense RNA and rely on RNA-dependent RNA polymerase to directly produce positive-sense RNA for protein synthesis. Since they never make a DNA intermediate or integrate into the host genome, they are not classified as retroviruses.