请问work on it had begun before my sister left 是什么句型

请问“work on it had begun before my sister laft.”一句中的work on it怎么讲,如题. 请问work on it had begun before my sister left 是什么句型 work on it had begun 为啥不用被动? work on it had begun before my sister left... Work on it had begun befor my sister left.请问这是什么从句?这个句子的引导词，主语，从句分别是什么？ work on 为什么可以放在句首?例如：Work on it had begun before my sister left. Work on it had begun before my sister left.分析句型Work on it had begun before my sister left.分析句型并翻译 这个句子为什么要用过去完成时?Work on it had begun before my sisiter left. work on it had begun before my sister left(这是什么句型? He kept on with his work ________ he had finished it.填空 Work on it had begun before my sister left.这句语法讲解下,有点迷糊. Work on it had begun before my sister left.是时间状语从句吗? 关于Work on it的疑问..Work on it had begun before my sister left.Work是主语..那么在这里Work on it是作为一个整体理解吗? Work on it had begun before my sister left中的WORK 不是动名词作主语 要加 用before改写I had already got home when it beg an to rain 请问had it work on it had begun befor my sister left.这句话的主语是什么?work 后为什么要加on.主要就是不明白work on it的句子成分,希望高手给讲讲 they had decided not to carry out necessary repair work on the tanker as it was due to be sold请问这里的as怎么翻译 做什么成分