The answer will be C because A response is a reactant for the plant and the question is asking about the light. B is incorrect because stimulus is how a plant reacts to nature for example gravitrophism and thingatropism also its asking about the light not the plant. D is incorrect because... come on now does it even make sense XD
begin by eliminating answers that don't make sense, such as "chosen one", then decide if each of the other ones make sense for it, the flower is responding to the lamp, so that means the lamp is not the response. It is the stimulus, because it is affecting the flower.
