What Aspect of the Germ Theory of Disease Has Influenced

What aspect of the germ theory of disease has influenced the behavior of most of the individuals in the picture below?

A) Coughing in a public place is socially unacceptable.
B) Disease-causing pathogens are communicable; they can spread from an infected individual to an uninfected individual.
C) Medications like antibiotics are a selection mechanism that ultimately strengthens the disease.
D) The pathogens that cause disease are too small to be seen without a microscope.