Concept:The hormone released during sudden fear or stress is known as the “fight or flight” hormone.Explanation:When a person is suddenly frightened, the body faces an emergency situation.The adrenal medulla responds by immediately secreting adrenaline into the bloodstream.Adrenaline increases heart rate, blood pressure, and energy supply.This prepares the body to either fight the danger or run away from it.Thus, the hormone suddenly released during fear is adrenaline.Answer:B. adrenaline