Festinger and Carlsmith Asked Their Participants to Tell Future Participants

Festinger and Carlsmith asked their participants to tell future participants that the study was exciting when, actually, it was very boring. Participants were then given $1 or $20 for their participation in the study. They were later asked for their real opinion of the study. What was the independent variable in this study?

A) The amount of money they received
B) Whether the tasks were moderately or extremely boring
C) How they really felt about the study
D) Whether they agreed or refused to lie to future participants