Which of the Following Is a Public Investment in Infrastructure

Which of the following is a public investment in infrastructure?

A) The federal government makes it easier for college students to obtain loans and this increases the number of students attending college.
B) Residents of a suburban housing development hire a private security force because they have been concerned about crime.
C) Southstar Steel has two office buildings separated by one- half mile. The company lays a fiber optic cable between the buildings to take advantage of new technology.
D) The city of Robesonia builds a new sewage treatment plant.