The Bison football team was the winningest program in NCAA Football history with thirty-three conference championships and eight national championships (1965, 1968, 1969, 1983, 1985, 1986, 1988, 1990) before moving to Division I Championship Subdivision in 2004. In January 2012, NDSU defeated Sam Houston State University in the NCAA Division I Football Championship game becoming the 2011 season National Champions. NDSU football is a major event in the city of Fargo and the region, averaging over 18,000 fans per home game.  The Bison play their home games at the Fargodome (cap. 19,287). In January 2013, NDSU football won the NCAA Division I championship title for a second year in a row, defeating Sam Houston again. They also defeated Kansas State and hosted College GameDay (football). In January 2014, NDSU defeated Towson to win its 3rd consecutive national championship in FCS football.  It is only the 2nd team in NCAA history to achieve this feat. NDSU also defeated FBS Iowa State for their 6th consecutive win over an FBS opponent and hosted ESPN College Gameday for the 2nd straight season. January 2015, for the 2014 season, NDSU defeated Illinois State to win its 4th consecutive national championship in FCS football. The feat had never been accomplished in Division I football.  In the 2015 season, NDSU defeated Jacksonville State for a record 5th consecutive NCAA Division I FCS national championship. No football team in the modern history of the NCAA has accomplished this feat. In the 2016 season, NDSU was defeated by James Madison, 27-17, who eventually went on to win the championship. Thus ending the Bisons reign of 5 consecutive championships. The following season the Bison went on to win the FCS National Championship again for the sixth time in seven years, by beating James Madison 17-13.
Question: Which years were national championships exactly two years apart?
Answer: 1983 | 1985 | 1986 | 1988 | 1990