Passage: Gabriel's father was a Lutheran originally from Hirschberg im Riesengebirge in Silesia, while his mother was a Catholic originally from Heilsberg in the Ermland (Warmia) region of East Prussia who had most recently lived in Königsberg; both parents came as refugees to West Germany during the flight and expulsion of Germans during the Second World War. Refugees from the eastern provinces often suffered prejudices in West Germany, and his mother's family were often disregarded as "Poles" in West Germany. Sigmar Gabriel has described his family history as a "wild story of flight and expulsion" and noted that his parents dealt with the trauma of expulsion in different ways. According to Gabriel, his father was physically and emotionally abusive to him and was an enthusiastic supporter of the national socialist ideology "until his dying breath;" However, Walter Gabriel never saw active service during the war due to suffering from polio. His mother was involved in relief and solidarity work for Poland during the period of martial law in Poland.Sigmar Gabriel attended school in Goslar, and served as a soldier in the German Air Force from 1979 to 1981.  He studied politics, sociology and German at the University of Göttingen from 1982 and passed the first state examination as a grammar school teacher in 1987 and the second state examination in 1989.

Question: When did Gabriel's father take his second state examination?
1989