A student is learning about infections that can occur in the human body. Infections could be caused by viruses, bacteria, and fungus. Which of the following statements correctly describes influenza, an infection caused by a virus?

The correct statement that describes influenza is:

**A. Influenza is caused by a virus because it is a living infectious agent that invades a host cell.**

However, it's important to note that while viruses invade host cells to replicate, they are considered "non-living" outside a host because they cannot carry out metabolic processes on their own. Therefore, the best phrasing would reflect that it is a virus (which is technically non-living outside a host) that causes the infection.

If looking specifically for the most accurate from the provided choices, none capture the complexity of virus definition perfectly, but ** is the closest in terms of describing the mechanism of infection.