John exercised in 5 minute intervals. The first set he exercised and recorded his heart rate. He rested for 20 minutes then put 15 extra kg onto his legs and again exercised for 5 minutes. He rested for 20 minutes. During the 3rd set he put on a total of 30 kg on to his legs and again exercised for 5 minutes. He measured his heart rate after each set and recorded the data in the table below. What was John's control set?
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4 points
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Set where John exercises with 15 kg added to himself
Set where John exercises with no weight added to himself
Set where John exercises for 0 minutes
Set where John exercises for 5 minutes