Final answer:
The author primarily uses dialogue to create conflict and advance the plot, which serves to define the theme of relying on knowledge and training over fear.
Step-by-step explanation:
The question asks how the author uses dialogue in a given excerpt. The purpose of dialogue in literature can often be multifaceted, however from the options provided and the reference material given, it seems that the dialogue is primarily used to create the conflict between Tom and Aunt Polly. The use of dialogue by Mark Twain advances the plot and defines the conflict, transitioning Twain's character from a state of confidence to one of anxiety and thus emphasizing his theme: the importance of relying on knowledge and training over fear.
The dialogue not only helps to develop characters but also shapes the purpose and theme of the passage. Moreover, Twain's use of dialogue provides authenticity to the narrative, inviting readers to experience the events first-hand. With regards to the conflict, it is a key element in creating reader interest and in the development of Twain's message to the audience.