Which of the following statements about viruses is true?

• A. HIV/AIDS is an example of a virus
• B. Viruses are never contagious
• C. Viruses can reproduce without a host
• D. All viruses cause disease in humans

Answer: (A)

Viruses are infectious agents that cannot reproduce on their own and must hijack a living cell’s machinery to make more viruses. Because they can move from person to person through various routes, many viruses are contagious. HIV is a virus, and it can cause AIDS, so the statement that HIV/AIDS is an example of a virus is true. The other ideas don’t fit: viruses being never contagious isn’t accurate since many are spread between people; viruses cannot reproduce without a host, which is a fundamental trait; and not all viruses cause disease in humans—some infect other organisms or may remain harmless or asymptomatic in people.