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。本题中的what引导主语从句what is known to us,并在句中做主语。It不能引导主语从句,which指特定范围之内的某一个;as不能引导名词性从句。What引导名词性从句,在句中做主语,宾语,表语等成分。句意:众所周知的是奥运会将在巴西的里约热内卢举行。故D正确。