In an experiment to determine the effect of exercise on pulse rate, a student checks his pulse rate before
and after exercising for several minutes. the purpose of checking his pulse rate before exercising is that it
(1) serves as the conclusion for the experiment
(2) is needed to justify the sample size
(3) serves as a control for the experiment
(4) is needed to formulate a hypothesis

3. 

in this experiment, the pulse rate before exercising serves as a control of the experiment. before exercise has been done, the pulse rate will be the one which is under normal circumstances, without varying any variable, and hence is the control for the experiment. to determine the change observed in pulse rate after exercising, the pulse rate after exercise will be compared to the control pulse rate. 

The blank would be speciation.