is known to us all is that America is a developed country the First World.A. Which; belong

问题补充：

is known to us all is that America is a developed country the First World.

A. Which; belonged

B. As; belonging to

C. What; belonging to

D. It; belonging

答案：

A. Which; belonged

B. As; belonging to

(答案→)C. What; belonging to

D. It; belonging

解析：第一空考查what引导的主语从句，在主语从句中，what做主语，第二空考查belong to做定语，belong to不能用被动，用现在分词做定语，句意是：众所周知的是美国是属于第一世界的发达国家。选C。