Jon Krakauer's Into the Wild is an example of juxtaposition because (C.) he includes snippets from poetry, postcards, and other sources at the beginning of each chapter.
Juxtaposition occurs in literature when a writer chooses to place two concepts, ideas or images next to each other in order to highlight their differences. In Into the Wild, Krakauer juxtaposes two different genres by opening each chapter with quotations from poetry, excerpts from interviews, postcards and other sources and contrasting them with narrative in order to bring differing perspectives together in one story.
Furthermore, each excerpt from poetry as well as the postcards and the interviews are closely connected to what is being told in each chapter. Therefore, Krakauer not only establishes a contrast between two genres in this book but he also establishes a link between two seemingly unrelated things.