A researcher performs the following classical conditioning experiment on several subjects. The experimental procedure for each subject is the same: 1. Subject relaxes for two minutes 2. Subject's pulse is taken. 3 Researcher taps a pencil on a desk five times 3. Subject performs jumping jacks for 30 seconds 4. Subject's pulse is taken, and they exhibit an increase in pulse rate. 5. Repeat steps 1-5 ten times 6. After two minutes of rest, the researcher taps a pencil on a desk five times, then takes the subject's pulse without exercising. It is elevated. What is the conditioned stimulus in this experiment? Subject exercises Experimenter taps pencil Subject's pulse is taken Subject rests for two minutes Subject exhibits an increase in pulse rate