英语语法问题ithasbeenestimatedthat=whathasbeenestimatedisthat=ashasbeenestimated,为什么可以这么替换,其中的语法是什么

Question

英语语法问题
it has been estimated that= what has been estimated is that=as has been estimated ,
为什么可以这么替换,其中的语法是什么

Answer 1

it has been estimated that...
it 是形式主语,that 从句是真正主语.that 从句可以移到句子开头,变为主语从句 That ...has been estimated.
what has been estimated is that...
其中的关系是what = that.把what 和 is 去掉,也能还原成 That...has been estimated.
as has been estimated,【estimated 后面有逗号隔开】
as 作关系代词,引导非限制性定语从句,先行词是整个主句,即逗号后面的句子.
例子：
It has been estimated that around a third of China's carbon emissions in 2005 were due to manufacturing exported goods.（据估计,2005年中国大约有1/3的碳排放是由于生产出口产品造成的.）
= What has been estimated is that around a third of China's carbon emissions in 2005 were due to manufacturing exported goods.
= As has been estimated,around a third of China's carbon emissions in 2005 were due to manufacturing exported goods.
= That around a third of China's carbon emissions in 2005 were due to manufacturing exported goods has been estimated.（这个结构不平衡）