To Investigate the Effects of Exercise on Mathematical Problem-Solving Ability

To investigate the effects of exercise on mathematical problem-solving ability, a researcher assigned participants to one of two groups. One group cycled on an exercise bike for one hour, and the other group performed no exercises. Afterward, both groups did a set of math problems and their performances were compared. In this experiment, the group that did not exercise is the

A) control group.
B) dependent variable.
C) independent variable.
D) intervening group.