Which statement is true regarding viruses?

Viruses are unique entities that occupy a gray area between living and non-living things. The statement that they can't replicate outside a host cell is indeed true. Viruses lack the cellular machinery necessary for reproduction and metabolic processes. To reproduce, they must enter a host cell, hijack the host's cellular machinery, and utilize it to replicate their genetic material and produce new virus particles. This reliance on a host cell for replication is a defining characteristic of viruses and distinguishes them from living organisms, which can typically reproduce independently. It also explains why scientists consider viruses to be obligate intracellular parasites.

The other statements are not accurate; viruses are too small to be seen with a light microscope, are not classified as living organisms in the traditional sense because they do not exhibit all characteristics of life, and do not have a cellular structure as they are made up of nucleic acid encased in a protein coat, rather than being composed of cells.