Please choose the correct answer to the question: A class is testing the effect of exercise on heart rate. The heart rate of two students before exercise is compared to their heart rate after running around a track. Which procedure will most likely help the class correctly compare the results of the two students?

Answer1: test students who are the same height Answer2: have the students run on the same day Answer3: measure the distance each student runs Answer4: have the students run for the same amount of time

Answer format: answer1/answer2/answer3/answer4
Answer: answer4