题目内容：

__is known to us all is that America is a developed country__the First World.
选Which; belonged to ,还是As; belonged to ,

优质解答

如果不是你的答案是错的,就是你的题抄写错了.我就直接说吧,下面3个结构不同,你要看清楚你的题是哪一个.
It is known to us that.
As is known to us, + 一个句子. （注意,us后面有一个逗号,这很重要）
What is known to us is that...
你这题应该是第三种,如果你题没抄错. 也就是选What , belonged to

追答：

如果你确定题没抄错，我肯定是What, belonging to