Sam Joins a Psychology Study Group at the Start of Semester

Multiple Choice

Sam joins a psychology study group at the start of semester. Each week the group members share the notes they took during classes, as well as interesting articles they have found. However, each week Sam claims to have been too sick or busy during the week to go to class or to take any notes. As such, Sam takes a copy of everyone else's notes from the study group but never contributes anything to the group himself. This is an example of:

A) the free-rider effect.
B) relative deprivation.
C) the commons dilemma.
D) public goods dilemma.