The purpose of an advertisement is to make people respond—to make them react ________an idea, such as helping to prevent forest fires, or to make them want to buy a certain product or service.
句意：广告的目的是让人们做出反应——让他们对某种想法做出反应，比如帮助预防森林火灾，或者让他们产生想买某种产品或服务的欲望。react to属于固定搭配，意为“对……做出反应”。因此，本题的正确答案为C。