This Graph Illustrates the Marginal Cost,marginal Private Benefit,and Marginal Social

This graph illustrates the marginal cost,marginal private benefit,and marginal social benefit of immunization against a contagious childhood disease.
One reason ____ children should be immunized is that

A) all;there are social benefits in addition to private benefits.
B) fewer than 150;immunizations pose risks.
C) fewer than all;medical care resources are scarce.
D) 100;that is the number at which marginal benefits equal marginal cost.