All of the provided responses are valid in illustrating how genre can affect the theme of a text. However, if you are looking for the most precise answer, it would likely be:
Genre affects which story elements the author will likely use to present the theme.
This is because different genres often come with specific conventions and tools that shape how themes are developed and expressed. For example, a romance novel might use emotional dialogue and character relationships to explore themes of love, while in a thriller, themes may be presented through suspenseful action and conflict.