The 30th olympic games,offically--as "London 2012 oympic gam

这题为什么用known?
因为 known as "被称为" ,是固定搭配,又是过去分词短语作定语修饰The 30th olympic games,相当于一个非限制生性定从:
The 30th olympic games,offically__as "London 2012 oympic games",
=The 30th olympic games,which was offically ( known ) as "London 2012 oympic games",
句意:第30届奥运会,被官方称为"伦敦2012届奥运会" ,将于7月27至8月12日举行.