The correct answer is B.
All links in the chain of infection must be intact for infectious disease to spread, therefore any break in this chain can help prevent the spread of disease.
Wrong Answers:
Option A. Infectious diseases are spread by microscopic pathogens. This is why they spread so readily, as you cannot see them, but they are everywhere (foods, inanimate objects, contained in respiratory droplets, etc.)
Option C. Infectious agents don't just include bacteria (which are treated with antibiotics), but also viruses, fungi, protozoa, yeast, etc, which require alternate treatments.
Option D. Some patients are much more susceptible to becoming sick when exposed to an infectious agent. Patients who are immunosuppressed or who have chronic medical problems are much more susceptible to life-threatening and severe infections.
Learning Point: All links in the chain of infection must be intact for infectious disease to spread, therefore, breaking this chain is the responsibility of all healthcare providers including medical assistants.