There are a lot of synonyms for discussion like: argument, conference, controversy, conversation, debate, dialogue, dispute, and quarrel for example.
Your answer is gentle souls are often disguised by rough exteriors. The others do not cover the overall theme of the book. Yes some rich and poor kids do not get along, but that is not an overall lesson. Also how often did they walk home alone. The story does not revolve around that. Last, Cherry was not a main character, she was not a main part of the plot. So your answer is once again the first one, it goes with the overall plot of the story.
Listing your ideas in order to generate a topic for your writing is B. brainstorming.
You just think of as many ideas as you can in order to find the perfect one for your essay or whatever it is that you are writing. Eventually, you will come up with an idea.
