C. I looked up at the audience and tried to swallow my nervousness.
A narrative essay tells a story, often from a first-person point of view, and includes personal experiences, emotions, and a sequence of events. Sentence C reflects this style—it uses "I," describes a personal moment, and includes emotional detail (nervousness), making it the most likely choice to come from a narrative essay. The other options are more informative, instructional, or fictional rather than personal storytelling.