D Stimulus
stim·u·lus[ˈstimyələs]NOUNstimuli (plural noun)a thing or event that evokes a specific functional reaction in an organ or tissue: "areas of the brain which respond to auditory stimuli"a thing that rouses activity or energy in someone or something; a spur or incentive: "if the tax were abolished, it would act as a stimulus to exports"synonyms: spur · stimulant · encouragement · impetus · boost · prompt · prod · incentive · inducement · inspiration · motivation · impulse · shot in the armantonyms: deterrent · discouragementan interesting and exciting quality: "she loved the stimulus of the job"