Which of the following statements is true about viruses?

Viruses are unique entities that differ significantly from living organisms. One of the defining characteristics of viruses is that they require a host cell to reproduce. In order to replicate, viruses must invade the cellular machinery of a host organism. Within this host, they hijack the cellular processes to produce copies of themselves, which can then infect other cells. This dependency on a host for reproduction is central to the biological understanding of viruses and distinguishes them from other microorganisms.

The other statements about viruses do not align with their fundamental characteristics. For example, viruses cannot live outside a host indefinitely; they can remain dormant in the environment for varying lengths of time but are generally inactive until they encounter a suitable host. Additionally, viruses cannot replicate independently; they lack the necessary machinery to do so. Lastly, viruses are much smaller than most bacteria, which is another reason they are categorized differently in biological classification.