question: What FIFA World Cup did the referee of the 28 May 2011 football match at Wembley Stadium participate in? 
answer: 2010 FIFA World Cup
context: Title: Statue of Bobby Moore, Wembley
  Passage: The Bobby Moore statue is a bronze sculpture of the former West Ham and England footballer Bobby Moore, situated outside England's national stadium, Wembley Stadium, in Wembley Park, north-west London.  It commemorates the life of Moore, who captained the only England side ever to win the World Cup, defeating Germany 4-2 in the 1966 FIFA World Cup Final held in England at the old Wembley Stadium, demolished in 2003.  Commissioned by the Football Association, it was unveiled outside the new stadium when it opened in 2007, fourteen years after Moore's death from cancer, aged 51.  Standing 20 ft tall on a stone plinth, it looks over spectators as they walk down Wembley Way into the stadium.  Sculpted by the Royal Sculptor Philip Jackson, it is Jackson's second piece featuring Moore, after the "World Cup Sculpture" unveiled in 2003.
  Title: 1966 FIFA World Cup Final
  Passage: The 1966 FIFA World Cup Final was the final match in the 1966 FIFA World Cup, the eighth football World Cup and one of the most controversial finals ever.  The match was played by England and West Germany on 30 July 1966 at Wembley Stadium in London, and had an attendance of 96,924.  The British television audience peaked at 32.30 million viewers, making the final the most watched television event ever in the United Kingdom.
  Title: 2011 UEFA Champions League Final
  Passage: The 2011 UEFA Champions League Final was a football match played on 28 May 2011 at Wembley Stadium in London that decided the winner of the 2010–11 season of the UEFA Champions League.  The winners received the European Champion Clubs' Cup (the European Cup).  The 2011 final was the culmination of the 56th season of the tournament, and the 19th in the Champions League era.
  Title: Viktor Kassai
  Passage: Viktor Kassai ("Kassai Viktor", : ; born 10 September 1975) is a Hungarian football referee.  He participated in the 2010 FIFA World Cup and refereed the 2011 UEFA Champions League Final.  He has been a full international referee for FIFA since 2003.
  Title: Carlos Vera
  Passage: Carlos Alfredo Vera Rodríguez (born June 25, 1976) is an Ecuadorian football referee.  He has been an international referee since 2006.  He has officiated matches in FIFA World Cup qualifiers, the Copa Libertadores, the Copa Sudamericana and the South American Youth Football Championship.  He was selected as a referee for the 2011 Copa América in Argentina and the 2015 Copa America in Chile.  In addition, he was appointed by FIFA to take charge of matches at the 2012 FIFA Club World Cup and the 2014 FIFA World Cup.  He was selected as the fourth official for the 2014 FIFA World Cup Final.
citations: Viktor Kassai 2011 UEFA Champions League Final