Which of the Following Best Illustrates the Free-Rider Problem

Which of the following best illustrates the free-rider problem?

A) A tollbooth is constructed at the entrance of a privately funded highway.
B) Individuals contribute toward a national defense program by paying taxes to the government.
C) Some homeowners in a mountain area refuse to contribute toward paving the area's access road.
D) You erect a fence around your swimming pool to keep out unsupervised children.
E) A steel mill does not consider the social cost of production while calculating its total cost of production.