John Thornton's intervention clearly demonstrates his role as a protector and compassionate figure in the story. By stepping in to stop Hal from abusing Buck, he shows his willingness to stand up for those who cannot defend themselves, highlighting his moral courage and kindness. This act of saving Buck from further abuse establishes Thornton as a key character who embodies empathy and strength, making it evident that he is a pivotal figure in the narrative. Therefore, the correct response is:
He saves Buck from further abuse, showing his compassionate and protective nature.