The sentence that BEST shows the way a person's body functions automatically take over in the event of an emergency is:
A. "At the sight of the tiger, your hypothalamus sends a message to your adrenal glands and within seconds, you can run faster, hit harder, see better, hear more acutely, think faster, and jump higher than you could only seconds earlier."
This sentence explicitly describes the automatic physiological responses that occur in the body during an emergency, making it the most relevant choice.