An Instructor Developed a Study to Determine Ways of Producing

An instructor developed a study to determine ways of producing more participation in his classes. In one class she provided free donuts everyday of class while in another she gave them nothing. She had her assistant takes notes on the number of comments and questions students made in each class. Which of these classes represent the control group?

A) The class not given the donuts.
B) The class given the donuts.
C) Other classes that are not part of the experiment.
D) Both classes would be considered the control group.