Which of the Following Is an Example of the Free-Rider

Multiple Choice

Which of the following is an example of the free-rider problem?

A) Both Fred and Wilma receive low-cost dental care at the local dental school,so neither of them pays the full cost of the care.
B) Elmer receives a free lunch from the local "Meals on Wheels" program because of his low monthly income.Yet his next door neighbor,Dorothy,is not eligible for the free lunch.
C) Max owns Fido,a large dog who barks whenever anyone walks near his house.Sally lives next to Max,and Fido's barking can be heard whenever anyone walks near her house,too.Thus,Sally receives free protection from burglars because of Fido's barking.
D) David purchases a burger at a fast food restaurant and gets a second burger free because the restaurant is having a buy one,get one free sale.