John was disappointed by Sarah’s rejection of his proposal.
The bolded passage is the rising action.
In a narrative, the rising action is the event, or series of incidents, which come directly after the exposition and before the climax. Its purpose is to set up suspense in the plot (in this fable, you can sense the tension in phrases like "he seized it with his paw and was about to kill it"). It is usually composed of character decisions and personality traits (here, the mouse's cunning and the lion's arrogance).
The correct answer, in my opinion, is A. The question of <em>When did the oral tradition begin? </em> would help the writer to narrow the focus of the paper.
In the case of questions B and D they are not related to the main topic of the paper. On the contrary, one of them focuses on the steam drill and the other on the melody of folk songs, neither of which are of great importance to the main aim of the paper which is to explore the historical background of the folk songs about John Henry.
In the case of C, I consider that it is not important whether John Henry was a real person or not. It's not the point of the piece of writing to arrive at that conclusion. Yet, it is more related to the topic than the other two questions.
In order to help the writer to narrow the scope of what is written, we should focus on the goal of the paper that is to deal with the question of <em>how folk songs about this subject have developed over time</em>. And for that purpose, trying to trace the beginning of the oral tradition is the best option to keep focused.