Which of these best demonstrates mutualism between certain types of bacteria and humans?

A. Intestinal bacteria obtain nutrients from the gut and produce vitamin K used by
humans.

B. Bacteria become resistant to antibacterial medication that humans use for treatment.

C. Invasive bacteria at an area of injury produce toxins that damage healthy tissues of
the human body

D. Bacteria in improperly prepared food is consumed by humans, causing food
poisoning.