Dr. Paul discovers a new chemical that he predicts will increase energy levels in hamsters. He designs an experiment to test his prediction. Dr. Paul separates 12 hamsters into two equal groups. He gives one group of hamsters the chemical but does not give the chemical to the other group. He keeps everything else about the hamsters' living environment the same. Over the next month, Dr. Paul measures the time that the hamsters spend running on their exercise wheels each day. He then calculates averages for these measurements, which are shown in the table below. Week 1 Week 2 Week 3 Week 4 Average Time Spent on Wheel by Hamsters Given Chemical 4.4 hours/day 5.1 hours/day 5.6 hours/day 5.3 hours/day Average Time Spent on Wheel by Hamsters Not Given Chemical 3.2 hours/day 2.5 hours/day 2.8 hours/day 3.0 hours/day The data that Dr. Paul collects during his experiment A. are not valid because experiments cannot be done on living organisms. B. are not valid because Dr. Paul did not use a control group in his experiment. C. contradict his prediction that the chemical will increase energy levels in hamsters. D. support his prediction that the chemical will increase energy levels in hamsters.