Dr McGlynn Is Conducting a Study on Reaction Time

Dr. McGlynn is conducting a study on reaction time. He allows subjects to exercise strenuously for either 0, 10, or 20 minutes. Next, subjects are seated at a table containing a red push button and a yellow light. Each subject is asked to push the button as soon as he or she sees the light flash. Dr. McGlynn measures the time it takes each subject to push the button after the light is lit. The control group in this study

A) did not exercise.
B) exercised for 10 minutes.
C) exercised for either 10 or 20 minutes.
D) exercised for 0, 10, or 20 minutes.
E) exercised for 20 minutes.