Which of the following is the best example of a response to external stimuli?

A. Pupils of the eyes dilate in the dark.

B. A flu virus infection results in vomiting.

C. When a person is hungry, his/her stomach growls.

D. A fatigued person responds by sleeping.

Answer - A. Pupils of the eyes dilate in the dark.

Reasoning - To start reason why it is answer A is because of the changes in the environment. Since the changes in the environment is dark, then your eyes will begin to dilate or get bigger in the dark to capture more light.