Which of the following is an example of a virus?

HIV, or Human Immunodeficiency Virus, is accurately identified as a virus because it falls under the category of infectious agents primarily composed of genetic material (RNA) encased within a protein coat. Unlike bacteria, such as Streptococcus and Escherichia coli, which are single-celled organisms that can reproduce independently, viruses require a host cell to replicate. HIV specifically targets the immune system, attacking CD4 cells, which can lead to acquired immunodeficiency syndrome (AIDS). This characteristic of hijacking host cellular machinery for reproduction is a defining trait of viral infections.

In contrast, the other options represent bacterial and fungal infections, which have distinct biological structures and life processes. Streptococcus is a type of bacteria that can cause infections like strep throat, and Escherichia coli is a bacterium often associated with foodborne illnesses. Ringworm, on the other hand, is caused by a fungal infection, further emphasizing the diversity in pathogenic organisms. Thus, the identification of HIV as a virus is based on its unique characteristics that set it apart from bacteria and fungi.