The physiology of emotion refers to:

A) changes that include changes in perception.
B) changes that include increased anger.
C) changes that include increased fist clenching.
D) changes that include increased heart rate.

The physiology of emotion refers to the physical changes that occur in the body in response to emotions. One example of such a change is an increase in heart rate. Therefore, the best choice is D - changes that include increased heart rate. Choices A, B, and C are not broad enough to capture the full range of physiological changes that occur with emotions.