The correct answer is: They show that the narrator is experiencing great pleasure throughout the passage.
Reasoning: The words "rapture" and "ecstasy" convey intense feelings of joy and pleasure, indicating that the narrator is deeply immersed in the beauty and experience of swimming in the ocean. Rather than expressing uncertainty or a change in mood, these terms highlight a profound satisfaction and enjoyment, enhancing the overall tone of exhilaration and delight in the passage.