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如果有be动词，谓语变身过程中丢掉be动词，本质就是变成了分词结构
When I was a little girl, I fell in love with science.
Being a little girl, I fell in love with science.
Because she knows what I need, she can provide a right answer.
Knowing what I need, she can provide a right answer.
As he was elected as the new president, he became prudent.
Elected as the new president, he became prudent.
As her work was done, she sat down for a cup of tea.
Her work done, she sat down for a cup of tea.
have， has， had + v-ed 统一变换成having + v-ed
本质是助动词代替了实意动词变形。
Because he has finished his home work, he is allowed to play video games.
Having finished his home work, he is allowed to play video games.
be动词后面是形容词，可以删掉be动词
状语从句到独立结构(absolute construction )
原文：https://www.cnblogs.com/long5683/p/13381233.html