The correct answer is "a basic idea within a text". In literature, a theme refers to the central message or main idea that the author is trying to convey through their work. It is the underlying concept or topic that the story revolves around and explores. Themes can be universal and resonate with readers on a deeper level, as they often reflect on human experiences, emotions, and values. By identifying the theme of a text, readers can gain a better understanding of the author's intentions and the overall significance of the work.