Which of the following best describes a characteristic of viruses?

Viruses are unique entities that do not possess cellular structures, which is a fundamental characteristic that distinguishes them from living organisms. Unlike bacteria, which are unicellular organisms equipped with the necessary machinery to carry out metabolic processes and reproduce independently, viruses lack this cellular organization. Instead, they consist of genetic material (either DNA or RNA) encased in a protein coat, and they rely completely on a host cell's machinery to replicate and propagate. This absence of cellular structures means viruses are classified as non-living entities when outside a host. They cannot perform metabolic functions on their own and need to infect a host cell to utilize the host's cellular machinery for reproduction and metabolism.