C

题目分析：句意:我们大家都知道的是2008年的奥运会将在北京举行。______is known to us all 是主语从句，它缺少主语，故用代词what来充当主语。这个句子的同义句为：（1）___As___is known to us all , that the 2008 Olympic Games will take place in Beijing.（2）_It_____is known to us all that the 2008 Olympic Games will take place in Beijing.故选C 。