大家好，请教一下： 在Practical English grammar 3rd 177.11说： Subject pronouns with forms of "be" can be left out after certain conjunctions, especially in a formal style. 例句： Start when ready. (= ... when you are ready.) Phone me if (it is) necessary. I'm enclosing my cheque for ￡50, as agreed. 而在518.1则说： Common expressions with "as" in place of a subject: as follows; as was expected; as was agreed; as is well known. 例句： I am sending you the bill, as was agreed. (NOT ... as it was agreed.) ----- 问题来了，我们可以看到这两句根本就是同样的句型： I'm enclosing my cheque for ￡50, as agreed. I am sending you the bill, as was agreed. 如果177.11说第一句可以看成是省略as後的主词及be动词，那就可以还原回去，变成： I'm enclosing my cheque for ￡50, as it was agreed. (因为177.11的前面两个例句也都可以还原) 可是在518.1却又说 I am sending you the bill, as was agreed. (NOT ... as it was agreed.) 但这明明就是同样的句型，177.11说主词、动词可以还原， 而518.1却说(NOT ... as it was agreed.)，似乎有些自相矛盾？ 照书中的逻辑来看，在这个句型里，下列三者应该是通用的啊？ ...as agreed. ...as it was agreed. （这两者的关系是as後面有无省略主词、动词） ...as was agreed. （这则可以理解成as是准关系代名词，代替主词it） 请教各位怎麽看？谢谢。 --

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