B. must be related.
The main point of having a thesis statement is to explain the certain topic. Topic Sentences are sentences that explain how the topic is related to your thesis statement so it must always be relevant.
The theme of "The Black Ball" that depends on having a Modernist narrator is that it is not good to be behind the black ball (eight ball) in pool, and in life, African Americans needed to play a game like pool, just to stay out of trouble. The ball is white represents who had a nice life and had the power because whites had all the power, yet with the changing times, the ball’s color might change too, just like the discrimination because Caucasians and African Americans.
The purpose of a conclusion paragraph is to "sum up your whole essay, or argument in one paragraph." Conclusion paragraphs usually consist of facts that you have already stated in your body paragraphs. Your final claim (which side of the argument you are on) and your counterclaim (the opposite side you are on) if you are writing a argument essay.
Hope this helps.