Answer:
OC) a topic sentence that states the main idea.
Step-by-step explanation:
OA) cause-and-effect signal words to indicate key relationships. is incorrect because not all essays have to do with things causing other things. An essay can be talking about many different things.
OB) a written appeal to the audience. is incorrect because the way the essay is written should be enough to appeal to the audience.
OD) three supporting paragraphs. is incorrect because an essay can have as many or as little paragraphs as you want/need.