20. In an investigation to determine the change in heart rate with increased activity, a biology
teacher asked students to take their pulses im-
mediately before and immediately after exercis-
ing for 2 minutes. The data showed an average
heart rate of 72 beats per minute before exercis-
ing and 90 beats per minute after exercising, if a
valid conclusion is to be made from the results
of this investigation, which assumption must be
made?
1 In most students, the average heart rate is not
affected by exercise,
2 Each student exercised with the same inten-
sity.
3 Exercise causes the heart rate to slow down