The correct answer is: C. Viruses (HIV)
AIDS is caused by the human immunodeficiency virus (HIV), a virus that attacks the body’s immune system. HIV is a retrovirus, which means that it uses RNA to replicate itself. Once HIV enters the body, it attacks and destroys CD4 cells, which are a type of white blood cell that are important for the immune system. As the number of CD4 cells decreases, the body becomes more and more susceptible to infections and diseases.
Bacteria are single-celled organisms that can cause a variety of diseases, including pneumonia, strep throat, and tuberculosis. Fungi are multicellular organisms that can cause diseases such as athlete’s foot, ringworm, and yeast infections. Protozoans are single-celled organisms that can cause diseases such as malaria, sleeping sickness, and toxoplasmosis.
While all of these organisms can cause disease, HIV is the only one that causes AIDS.