A. Aldosterone: Aldosterone is a steroid (mineralocorticoid) from the adrenal cortex that helps maintain blood volume and blood pressure during prolonged stress; although cortisol (a glucocorticoid) is the primary mediator of the resistance stage, aldosterone is the best choice among the options because it is part of the longer-term adrenal (cortical) response seen in the resistance stage. B. Norepinephrine: Norepinephrine is a sympathetic neurotransmitter released rapidly during the alarm (immediate) stage of the stress response; its effects are fast and short-lived, so it is not the dominant mediator of the resistance stage. C. Angiotensin: Angiotensin II is part of the renin-angiotensin system that affects blood pressure and stimulates aldosterone, but it is not the principal hormone characterizing the resistance stage. D. Epinephrine: Epinephrine (adrenaline) is released from the adrenal medulla as part of the immediate “fight-or-flight” alarm response; it acts quickly and is not the dominant hormone in the longer-term resistance phase.