Students did an experiment comparing the activity of four different enzymes, A, B, C, and D. The results are represented in the graph below. A valid conclusion based on the information in the graph is that... A) the pH of some enzymes changes as the temperature changes.

B) enzymes change color in proportion to the rate of activity.

C) a difference in the pH of an environment changes enzyme activity.

D) enzyme activity causes acids to change into bases over time.