it用来充当形式主语或形式宾语，后面的真正主语或真正宾语通常是不定式结构、动名词或名词性分句。It的这种用法叫作先行it。 eg. It is quite important for us to form a good studying habit. I think it important to finish the task in time. it用来充当形式主语，后置的真正主语往往可以取代先行it的位置，出现在句首。 Eg. To form a good studying habit is quite important for us 并非所有先行it结构都可转化，下边句子只能作如下转化。 eg. It seems that John is not coming after all. John doesn’t seem to be coming after all. Cleft it : Task 1. 句子的基本结构 2 .分裂句的本质 3 . 分裂句的结构 4 .假拟分裂句 句子结构 主语 谓语 已知信息 新信息 末端中心 末端重心 Eg. I told him the news yesterday. 分裂句的本质 Eg. I told him the news yesterday. Eg. It is I that told him the news yesterday 分裂it 分裂句是以it为引导词的强调句型。它的结构形式是：It be 的一定形式 中心成分＋that /who分句。通过这种结构可以强调除谓语动词以外的大多数句子成分。说话人通过分裂句分别强调主语、间接宾语、直接宾语、状语，使之成为信息中心。分裂句中的谓语可以采取复杂形式 Eg. It is I who am to blame. It may have been at Christmas that John gave Mary a handbag. It was in Shanghai that I got my Master’s Degree. 主语补语通常不作分裂句的中心成分。宾语补语可以这样用。 It is beautiful that she is. It is Chairman of the committee that they elected him