Respuesta :
A stressor is an event/situation that causes a strain on your body/mind.
A eustress is a stress but it's determined to be a good form of stress.
The fight/flight response is a physiological reaction that our body reacts to when put in a difficult situation.
The right answer is Stressor.
Stressors (or stress factors) are all internal and external stimuli that cause stress and thereby cause the affected individual to a reaction of active adaptation. The organism interprets the stimuli that affect it and their effects on the respective situation and assesses them either positively or negatively.