You will be given a definition of a task first, then some input of the task.
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: During what year or years did the Anglo-Irish Treaty occur? Passage:After he qualified he travelled to Canada and during World War I he enlisted in the 19th Alberta Dragoons as a private and was commissioned to the Royal Marine Artillery. He had a distinguished military career and was awarded the Distinguished Service Order by the British Government and the Croix de Guerre. He had lost an eye and was badly wounded in both legs during his years at the front. His cousin, Robert Barton, had resigned as a British Officer after the 1916 Easter Rising and was elected as a Sinn Fein Teachta Dala at the 1918 general election for the West Wicklow constituency. His other cousin, Erskine Childers, used his yacht, the Asgard, to transport guns from Germany to Ireland on behalf of the Irish Volunteers. He too was a former British Army Officer that became more sympathetic with the cause of Irish independence after the events of the Rising. Robinson took an active part in the War of Independence in Wicklow. He opposed the Anglo-Irish Treaty and fought on the Republican side in the Civil War. He was present in Annamoe, County Wicklow when his cousin, Erskine, was arrested by Free State Troops and taken to Dublin which would result in his court-martial and execution. Robinson was himself arrested in 1922 and spent forty days on hunger strike during his eighteen months' internment in Mountjoy jail.
Links: a. Anglo-Irish Treaty b. Court-martial c. Germany d. 19th Alberta Dragoons
Output:
a