Which statement about RNA viruses is true?

• A. They replicate in the nucleus using DNA-dependent DNA polymerase.
• B. They replicate in the cytoplasm using RNA-dependent RNA polymerases.
• C. They replicate in mitochondria using DNA polymerases.
• D. They replicate outside the cell.

Answer: (B)

RNA viruses rely on RNA-dependent RNA polymerase to copy their genomes, because human cells don’t have enzymes that replicate RNA from an RNA template. This enzyme is provided by the virus, either packaged with it or encoded in its genome, and becomes active soon after the virus enters the cell. That’s why replication occurs in the cytoplasm for most RNA viruses—the viral polymerase operates there to synthesize new RNA. The other ideas don’t fit because DNA polymerases copy DNA from DNA templates, mitochondria aren’t the typical site of viral replication, and viruses must replicate inside a host cell rather than outside it. Contextually, there are exceptions where certain RNA viruses bring their replication machinery into specific compartments, but the general principle remains: replication in the cytoplasm using an RNA-dependent RNA polymerase.