An excerpt from the procedure of an experiment is shown below. "In order to determine the effectiveness of various enzymes on the rate of a reaction, we prepared six samples, adding a different enzyme to each sample. Each sample was kept at 70°C for the duration of the reaction..." Based on the information in the excerpt, which of the following is true? A. The samples should not have been kept at the same temperature.
B.
One sample should have had no enzyme and acted as a control.
C.
There were no variables present in the experiment.
D.
The experiment will not give useful results because all enzymes become inactive above 67°C.