is known to us is that the Olympic Games will be held in Rio de Janeiro Brazil.A. It

问题补充：

is known to us is that the Olympic Games will be held in Rio de Janeiro, Brazil.

A. It

B. Which

C. As

D. What

答案：

A. It

B. Which

C. As

(答案→)D. What

解析：考查主语从句，分析句子可以发现，第二个is是这句话的谓语，前面的is指主语从句的谓语，that引导的是表语从句，在主语从句中is前面缺少主语，用what连接主语从句，句意：我们都知道的事情是，奥运会在里约热内卢举办。选D。