Given the task definition and input, reply with output. In this task, you're given a question, a context passage, and four options which are terms from the passage. After reading a passage, you will get a brief understanding of the terms. Your job is to determine by searching and reading further information of which term you can answer the question. Indicate your choice as 'a', 'b', 'c', or 'd'. If you think more than one option is plausible, choose the more probable option to help you answer the question.

Question: How long did the arbitration in which the islands played a small role last? Passage:The military history of the Aleutian Islands began almost immediately following the purchase of Alaska from the Russian Empire by the United States in 1867. Prior to the early 20th century, the Aleutian Islands were essentially ignored by the United States Armed Forces, although the islands played a small role in the Bering Sea Arbitration when a number of British and American vessels were stationed at Unalaska to enforce the arbitrators' decision. By the early 20th century, a number of war strategies examined the possibility of conflict breaking out between the Empire of Japan and the United States. While the Aleutian Islands were seen as a potential staging point for invasions by either side, this possibility was dismissed owing to the islands' dismal climate. In 1922, the Washington Naval Treaty was signed, after which the United States Navy began to take an interest in the islands. However, nothing of significance was to materialize until World War II.
Links: a. Unalaska, Alaska b. United States c. Aleutian Islands d. Bering Sea Arbitration
d