Detailed Instructions: In this task, you are given a context, a subject, a relation, and many options. Based on the context, from the options select the object entity that has the given relation with the subject. Answer with text (not indexes).
Problem:Context: The 2012 Summer Olympics, formally the Games of the XXX Olympiad and commonly known as London 2012, was a major international multi-sport event celebrated in the tradition of the Olympic Games, as governed by the International Olympic Committee (IOC). It took place in London and to a lesser extent across the United Kingdom from 25 July to 12 August 2012. The first event, the group stage in women's football began on 25 July at the Millennium Stadium in Cardiff, followed by the opening ceremonies on 27 July. 10,768 athletes from 204 National Olympic Committees (NOCs) participated., Vassiliki Arvaniti (born March 17, 1985 in Athens, Greece) is a female beach volleyball player from Greece, who won the gold medal at the 2005 European Championships in Moscow, Russia and the 2007 European Championship in Valencia, Spain, partnering Vasso Karadassiou. She represented her native country at the 2004 Summer Olympics in her home town, with Thaleia Koutroumanidou. At the 2008 Summer Olympics, she competed with Karadassiou. Later, she took part in the 2012 London Olympics with Maria Tsiartsiani who was later injured. Since 2013, her teammate has been Peny Karagkouni who used to play indoor volleyball., Maria Tsiartsiani (born 21 October 1980 in Thessaloniki) is a Greek Olympic beach volleyballer. She competed at the 2008 Summer Olympics, partnering with Efthalia Koutroumanidou. At the 2012 Summer Olympics, she competed with Vassiliki Arvaniti., Efthalia `` Thaleia '' Koutroumanidou ( Greek :  ``  ''  ; born 7 October 1982 in Volos ) is a Greek Olympic beach volleyballer at the 2008 Summer Olympics and the 2004 Athens Olympics . She is partnered with Maria Tsiartsiani ., Beach volleyball is a team sport played by two teams of two players on a sand court divided by a net. It has been an Olympic discipline since the 1996 Games., Subject: efthalia koutroumanidou, Relation: participant_of, Options: (A) 2004 summer olympics (B) 2008 summer olympics (C) 2012 summer olympics (D) sport
Solution:
2004 summer olympics