The technique you are describing is known as flashback. However, among the options you've provided, none specifically define that term.
- Foreshadowing refers to hints or clues about what will happen later in the story.
- Tone refers to the author's attitude toward the subject or audience, which is conveyed through word choice and style.
- Irony involves a contrast between expectation and reality, often used to highlight discrepancies between appearance and truth, or between what is said and what is meant.
If you're looking for the closest related concept to your description in the context of narrative techniques, "flashback" is the term to use, but it's not an option presented here. If required to select from the given options, none would be appropriate for the specific technique of "introducing information by shifting to an earlier time."