英语语法问题it has been estimated that= what has been estimated is

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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

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）

六级真题it has been estimated that theearth's surface temperatur 英语语法1.it has been estimated that if the bridge were packed w it is estimated that more than 50 million people have been i it is/has been= 分析下services growth is estimated to have been 19.1%. 一到英语语法题It is estimated that the novel will be _____ of his b 两个英语语法填空.It is estimated that 60% of all journeys used to be 请教一个OC IS问题It has recently been discovered that和It is a rece 英语主谓一致问题It is estimated that the number of foreigners coming 翻译 that is just the way it has always been 英语翻译Although the prevailing supposition has been that it is it has been a long time. what is up