什么是独立主格结构.什么时候用.怎么用.给我举个例子

独立主格结构一般在句子中做状语,是由一定的从句变换而来,主从句主语不一致的情况下用,结构有：n.+ to do/ doing/ done/ adj./adv./介词短语,有时还要注意时态语态（having done/having been done,to do/ to be done) 其他结构：there being / it being + n.
eg.
there being no buses,let's walk home.
it being Sunday,they had no classes.
meeting (being) over,our headmaster stepped out of the meeting room.
weather permitting,we will go out to play.= if time permits,we will go out to play.
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团结