Which of the following is a characteristic of viruses?

• A. They are composed only of proteins without any nucleic acids.
• B. They can reproduce independently in the environment.
• C. They require a host cell to replicate.
• D. They possess both DNA and RNA in the same particle.

Answer: (C)

Verified step by step guidance

1. Understand the basic structure of viruses: Viruses are composed of nucleic acids (either DNA or RNA) enclosed in a protein coat called a capsid. They do not contain both DNA and RNA simultaneously in the same particle.
2. Recognize that viruses lack the cellular machinery necessary for independent reproduction, meaning they cannot reproduce on their own in the environment without a host.
3. Recall that viruses require a host cell to replicate because they rely on the host's metabolic machinery to synthesize viral components and assemble new virus particles.
4. Eliminate incorrect options by comparing them to known viral characteristics: viruses are not composed only of proteins (they have nucleic acids), they cannot reproduce independently, and they do not possess both DNA and RNA in the same particle.
5. Conclude that the defining characteristic of viruses among the given options is their dependence on a host cell for replication.