Final answer:
Candy refusing to shoot his old dog and remaining silent after the event.
Step-by-step explanation:
The action that BEST develops the theme of loneliness in the text is option B) Candy refusing to shoot his old dog and remaining silent after the event. This action highlights the isolation and loneliness experienced by Candy as he feels the pain of losing his loyal companion. By refusing to speak up or defend his dog, Candy is symbolically illustrating his own fear of abandonment and loneliness.