Rainsford's sense of honor is so strong that he refuses a deal that would help him.
Rainsford does not believe that hunting humans is the correct thing to do. He is horrified with the knowledge of Zaroff's new choice for game on the island. In the interaction between Zaroff and Rainsford, Rainsford refuses to agree to the terms Zaroff proposes because Rainsford will not keep quiet about Zaroff's murders.
His sense of morality leads him to refuse to hunt human beings with Zaroff.
Rainsford did not choose to jump overboard. His morality keeps him from accepting Zaroff's deal. He is not arrogant and does not make Ivan his enemy. There is only one correct answer for this question.
It establishes the setting as a mysterious and isolated place.
The beginning of the story introduces the mysteriousness of Ship-Trap Island. The hunters discuss how ships have anchored at the island and never returned. The island is also shrouded in fog and darkness.
