The best answer to how the author uses Gortsby's initial encounter with the elderly man to develop the story's theme is:
d. the author reveals to readers that Gortsby's perception of the elderly man was incorrect.
In "Dusk," the theme revolves around the theme of judgment and the tendency to misinterpret others based on superficial observations. Gortsby's initial perceptions of the elderly man lead him to form a biased opinion that ultimately proves to be wrong, highlighting the dangers of making quick judgments about people's characters. This twist not only emphasizes the theme but also creates a moment of irony in the story, enhancing the reader's understanding of Gortsby's character and the broader human experience.