An infectious agent that cannot reproduce outside living cells is a what?

• A. Virus
• B. Volume
• C. Verbal
• D. Virulent

Answer: (A)

Viruses are obligate intracellular parasites: they cannot reproduce outside living cells because they lack the full cellular machinery needed for replication. They carry genetic material—DNA or RNA—but rely on a host cell’s enzymes and ribosomes to replicate and assemble new viral particles. Outside a host, viruses are inert and cannot multiply. That’s why the infectious agent described is a virus. The other options don’t fit: volume is a measure of space, verbal relates to speech, and virulent describes how harmful a pathogen is, not the type of infectious agent.