Why Might the Marginal Social Benefit of Crime Control Decrease

Why might the marginal social benefit of crime control decrease as additional units are provided?

A) The feeling of security increases as more crime control is provided, therefore people are willing to pay more for additional units.
B) The opportunity cost of crime control decreases as more is provided, therefore people are willing to spend less for additional units.
C) As people feel safer because of more crime control, they do not place as great a value on a little more safety.
D) The opportunity cost of crime control increases as more is provided, however, people are willing to spend more for additional units.