"You start an exam and realize that you did not study enough for it. You find it difficult to concentrate because your heart is racing, your stomach seems tied in a knot, you are breathing too quickly, and your mouth is dry. Most likely, you are experiencing the effects of the ."

Sympathetic Nervous System.

Explanation:

  The primary function of this system is to maintain and regulate the rate of unconciousness in a body system; which includes controlling the body response to involuntary harmful occurences. It sets the body system ready for any form of physical and mental stress. And their is a pump of blood into the adrenaline, boasting the rate of this actions.

i think it’s c but i might be wrong. if i am let me know! have a good rest of your day as well!