is known to us all is that the Olympic Games will take place in London.A. ItB. WhatC.

问题补充：

is known to us all is that the Olympic Games will take place in London.

A. It

B. What

C. As

D. Which

答案：

A. It

(答案→)B. What

C. As

D. Which

解析：通过分析句子结构，可知这个句子中包含一个主语从句和一个表语从句。引导词在主语从句中作主语，且表示什么的含义，故用What。