Year years 1970 3 1971 3 1972 3 1973 3 1974 3 1975 3 1976 3 1977 3 1978 3 1979 3 1980 3 1981 3 1982 3 1983 3 1984 3 1985 3 1986 3 1987 3 1988 3 1989 3 1990 3 1991 3 1992 3 1993 3 1994 3 1995 4 1996 4 1997 4 1998 4 1999 4 2000 4 2001 4 2002 4 2003 4 2004 4 2005 4 2006 4 2007 4 2008 4 2009 4 2010 4 2011 4 2012 4 2013 4 2014 4 2015 4 2016 4 2017 4 2018 4 2019 4 2020 4 2021 4 2022 4 2023 4