The central idea in the story is about how she has to take care of her older brother Raymond because he is disabled. The pivotal moment, in the end, shows Squeaky learning to be less self-centered by giving up her competitive running in order to start training Raymond for running.
That would be C, imagery.
When I read the passage, I can clearly imagine the wharf Twain is describing.
Through Holly's words: She is down and frustrated
through Holly's thoughts: She is negative and doesn't believe in herself.
through the actions of other characters: She needs someone to push her and support her and tell her what she needs to hear to continue learning