Concept:The blank needs a phrasal verb meaning to switch off or extinguish a light.Explanation:"Put out" means to extinguish or switch off a light or fire: "We always put out the lights before going to bed.""Off" and "out" alone are not verbs, so the sentence would have no main verb."Put off" mainly means to postpone ("put off the meeting").Key point: In standard English we put out a light or a fire; "put off" is best kept for postponing.Answer:Option C (put out)