The nervous system is responsible for our fight-or-flight response.

The sympathetic nervous system (SNS) is responsible for our fight-or-flight response. The main function of this nervous system i to mobilise the body's fight or flight response. Action include: acceleration of the heart rate,sweating, decreasing motility of the large intestine, fast breathing, constricting blood vessels...

out of the choices i'd say d the ability to set goals, mainly because to desire to continue you need motivation but it isn't motivation in that part, but setting goals means you have an endgame and you want to reach it which sums up motivation.

answerrunning;