Question: What is the nationality of the soccer player who was the head coach of the under-21 football team that has been playing since 1976?

full_context: Document 1: Denmark women's national junior handball team: The Denmark women's junior national handball team is the national under–19 Handball team of Denmark. Controlled by the Danish Handball Federation it represents Denmark in international matches.
Document 2: East Germany national under-21 football team: The East Germany national football team was the national football team of the German Democratic Republic. Following the realignment of UEFA's youth competitions in 1976, East Germany's Under-21 team was formed. The team played until 1990, until East Germany ceased to be a separate country after the reunification of Germany.
Document 3: National under-21 football team: A National under-21 football team represents the second-highest stage in European international football competition. Only Europe (UEFA) uses an under-21 age limit, and only for men. FIFA, the sport's worldwide governing body, runs competitions for both men and women in the under-20 age group. Among FIFA's continental confederations, CONCACAF and CONMEBOL hold U-20 championships for men, while the Asian Football Confederation (AFC) and Oceania Football Confederation (OFC) do not conduct U-20 championships, with their highest youth competitions for men being at under-19 level. For women, UEFA and the AFC run under-19 championships instead of under-20; CONCACAF, CONMEBOL, and the OFC run under-20 championships; and the CAF's under-20 "championship" is strictly a World Cup qualifier and currently has no championship match, as that confederation receives more than one berth in the U-20 Women's World Cup.
Document 4: Kasper Dolberg: Kasper Dolberg (born 6 October 1997) is a Danish professional footballer who plays as a forward for Ajax and the Denmark national team. Dolberg made his senior debut at Silkeborg IF in May 2015. He joined Ajax in July 2015 and made his debut for the club in July 2016. He represented Denmark at under-16, under-17, under-19 and under-21 level before making his senior international debut in November 2016.
Document 5: Bjørn Kristensen: Bjørn Kristensen (born 10 October 1963) is a Danish former professional football player who played for Danish club Aarhus Gymnastikforening and English club Newcastle United, where he was nicknamed "Benny". He played 20 matches and scored two goals for the Danish national team, and represented his country at the 1988 European Championship.
Document 6: Kristian Bak Nielsen: Kristian Bach Bak (né Bak Nielsen; born 20 October 1982) is a retired Danish professional footballer. Bak usually played central defender, but he has a past as a striker. He has played one game for the Danish under-21 national team.
Document 7: England national under-21 football team: England's national Under-21 football team, also known as England Under-21s or England U21(s), is considered to be the feeder team for the England national football team.
Document 8: Keld Bordinggaard: Keld Tande Bordinggard (born November 22, 1962) is a Danish former football (soccer) player. He was the head coach of the Danish national under-21 team from July 2006 until the U21 European Championship in June 2011. As a player, he most notably played professionally for Danish clubs Odense Boldklub and Silkeborg IF, both with whom he won the Danish football championship. Keld Bordinggaard played four games for the Danish national team from 1983 to 1990.
Document 9: Denmark national under-21 football team: The Denmark national under-21 football team has played since 1976 and is controlled by the Danish Football Association. Before 1976, the age limit was 23 years.
Document 10: Kasper Bøgelund: Kasper Bøgelund Nielsen (born 8 October 1980 in Odense) is a retired Danish footballer. He last played as a right back for AaB in the Danish Superliga. Bøgelund has played 17 games for the Danish national team, and he represented Denmark at the 2002 FIFA World Cup and 2004 European Championship.
Document 11: Denmark women's national youth handball team: The Denmark women's youth national handball team is the national under–17 Handball team of Denmark. Controlled by the Danish Handball Federation it represents Denmark in international matches.
Document 12: Sweden national under-23 football team: The Sweden national under-23 football team (also known as Sweden Olympic football team from 1992) is the football team representing Sweden in Olympics and is controlled by the Swedish Football Association. Between 1952 and 1976, the Swedish U23 team was the main Swedish national youth team and represented Sweden in the UEFA European Under-23 Championship. Sweden made their first and only European Under-23 Championship appearance in 1972 and was knocked out in the quarter-finals. In 1976 the European Under-23 Championship was changed to be an Under-21 competition, so the Swedish U23 team became defunct and was replaced by the Sweden national under-21 football team.
Document 13: Klavs Bruun Jørgensen: Klavs Hørlykke Bruun Jørgensen (born3 April 1974) is a Danish handball player and coach for the Denmark women's national handball team. As a player, he led FCK Håndbold to the Danish championship in May 2008. He has previously played for many years by Danish Handball League rivals GOG, with whom he won two Danish titles. For a short period he played for German league side SG Wallau-Massenheim
Document 14: Morten Wieghorst: Morten Wieghorst (born 25 February 1971) is a Danish association football manager and former player. He is currently head coach for AaB. He is the former head coach of the Denmark national under-21 football team and FC Nordsjælland in the Danish Superliga whom he guided to the 2010 and 2011 Danish Cup trophy.
Document 15: West Ham United F.C. Under-23s: West Ham United F.C. Under-23s, formerly West Ham United F.C. Under-21s is the most senior of West Ham United's youth teams. The Under-23 team is effectively West Ham United's second-string side, but is limited to three outfield players and one goalkeeper over the age of 23 per game following the introduction of new regulations from the 2012–13 season. They play in Premier League 2 and also compete in the Checkatrade Trophy.
ground_truth: Danish