This Figure, Based on Data Collected by the National Institute

This figure, based on data collected by The National Institute of Allergy and Infectious Diseases, graphically illustrates that a disease is less likely to spread to vulnerable members of a population if most of the population is immunized against the disease. This phenomenon occurs because

A) when fewer individuals in the population are likely to become infected, fewer people are able to spread the disease, and the vulnerable members of the population are less likely to come in contact with contagious individuals.
B) if more individuals in the population become infected, fewer people are able to spread the disease, and the vulnerable members of the population are less likely to come in contact with contagious individuals.
C) if more individuals in the population become infected, more people are able to spread the disease, and the vulnerable members of the population are less likely to come in contact with contagious individuals.
D) when none of the population is immune to the disease, no one will contract the disease and therefore pass it on to the vulnerable members of the population.