Answer
a.
Work Step by Step
Option b. is incorrect. Malaria is caused by a type of protist and affects the red blood cells.
Option c. is incorrect. Tuberculosis is caused by bacterium that infect the lungs first.
Option d. is incorrect. MRSA is a type of bacterial infection that is resistant to antibiotics.
Option a. is the only correct option. The HIV virus infects the human immune system, making it too weak to deal with other pathogens that normally may not cause serious illness in healthy individuals.
