Matthew just had an unpleasant encounter with his chemistry instructor. As he walks angrily away, he notices that his heart is pounding rapidly and he is perspiring. As he passes a mirror he notices that his face is also beet red. Matthew's system is responsible for this physical reaction.

Sympathetic.

Explanation:

The sympathetic system is a part of our autonomic nervous system which regulates some of the important functions of our body such as heart rate, blood pressure, blood vessels, etc. These actions are taking place unconsciously and thus it is also known as the involuntary nervous system. These actions usually happens in a situation such as fight-or-flight.

In the given case, Matthew's face turned beet red because of the sympathetic system which accelerated his bodily functions such as blood rate, blood pressure, etc that regulated blood to his muscles and making his face turn beet red.

Thus, the correct answer is the sympathetic system.

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