If you use the process of elimination it's a lot easier to figure this out. so let's break this down, if you start with the conflict you know that it can't be the answer because the conflict is pretty much THE MOST IMPORTANT PART of a story, so that's not it. It wont be the setting because the setting plays a big role in seeing what the character can use and who they will see, so that's not it either. These two are both important so you have to pay attention to the words "MOST LIKELY" as you always should with every question that has it. So the antagonist pays a pretty big role because without it the character most likely wouldn't learn the lesson or point of the story.
