What does irrigate means?

Which of these excerpts is most clearly an example of narrative poetry? a. “in xanadu did kubla khan/a stately pleasure dome decree…” b. “and all that’s best of dark and bright/meet in her aspect and her eyes…” c. “who can contemplate fame through clouds unfold/the star which rises…” d. “one shade the more, one ray the less/had half impaired the nameless grace…”