Every Few Months,public Radio Announces a Call for Pledge Support

Multiple Choice

Every few months,public radio announces a call for pledge support.During this time,it asks listeners to contribute to their local public radio station.Although they raise money during this time,it often falls short of the amount they wish to raise because:

A) they do not make the pledge period long enough.
B) listeners know they will be able to hear public radio,even if they don't contribute.
C) public radio free-rides on the listeners.
D) the marginal social cost equals the marginal social benefit of public radio listening.