I think the blank is an audience, because if your writing a PERSUASIVE essay, your trying to persuade a specific audience to agree with you on an opinion or trying to complete a certain action, so D makes the most sense, in my mind at least
In the pivotal case of Plessy v. Ferguson in 1896 the U.S. supreme court ruled that racially separate facilities, if equal, did not violate the Constitution. segreation, the court said, was not discrimination.