(
课件网) Unit 4 Breaking boundaries it as an empty subject 1.To understand the general knowledge of it as an empty subject. 2. To be able to use it as an empty subject in proper situations. Learning aims 观察句子 1．But it is vital not to take any chances. 2．It is important to remember that Ebola doesn't respect national boundaries. 3．It is so inspiring to have colleagues like Wilton... 4．It is no use crying over spilt milk. 5．It is no good sighing about your failure; you'd better start again. 6．It makes me angry that he doesn't study hard. 7．It is not clear whether they consider this opinion or not. Leading-in 1．句1、2、3中的it作形式主语，真正的主语是后面的_____。 2．句4、5中的it代替的真正的主语是_____。 3．句6、7中的it代替的真正主语是由_____或_____引导的从句。 Leading-in to do不定式 V-ing短语 whether that 当主语部分相对于谓语部分而言太长时，常把主语部分移到句尾，在主语的位置放上it。it 没有具体的意义，仅用于使句子显得平稳，不头重脚轻。it 作形式主语时常代替三种语法结构： 不定式(短语)、v. ing(短语)和从句。 一、it代替不定式(短语)作形式主语 1．It＋be＋名词/名词词组＋to do sth.，这类名词有a habit、a pleasure、a fact 等。 ◆It is not a good habit to stay up too late. 睡得太迟不是个好习惯。 2．It＋be＋形容词＋(for sb.)＋to do sth., 这类形容词用来描述不定式行为本身的性质,有necessary、wrong、right、important、difficult、easy等。 ◆It is necessary for you to be fully aware of your own shortcomings. 充分认识自己的缺点是很必要的。 3．It＋be＋形容词＋of sb.＋ to do sth.，这类形容词用来描述不定式行为者的性格、品行等时，不定式前常可加一个由of引起的短语。这类句型所涉及的常用形容词有foolish、kind、good、polite、selfish等。 ◆It was foolish of you to behave like that. 你那种表现真是太蠢了。 4．It＋takes＋sb.＋时间或金钱＋to do sth.，这是一个表示某人花了多少时间或金钱做某事的句型。其中it是形式主语，代替后面的不定式，句中的sb.也可省略。 ◆It took thousands of people many years to build the Great Wall. 成千上万的人花了很多年才建成了长城。 二、it代替v. ing(短语)作形式主语 It＋be＋名词/名词词组＋ doing sth.，这类名词有(no) good、(no) use、(no) time、a waste of time、fun等。 ◆The doctor told us that it is no good eating too much meat. 医生告诉我们吃太多的肉没有好处。 【温馨提示】 it作形式主语代替v. ing(短语)时，往往限于以下句型中：It is no good/no use/fun/a waste of time...中，如不是上述句型，在将v. ing(短语)移到句尾用it作形式主语时，v. ing(短语)要改为不定式。 【即学即练】单句语法填空 (1)It is necessary for high school students (learn) another foreign language. (2)As far as I'm concerned, it's no use (argue) with him, he won't change his mind. (3)It is essential you to accomplish the papers before Sunday. (4)It's clever you to work out the maths problem. of to learn for arguing 三、it代替从句作形式主语 用it 作形式主语的结构主要用于下列句型： 1．It＋be＋名词＋从句，这类名词有a fact、a surprise、an honor、a pity、a wonder、common knowledge等。 ◆It is common knowledge that the full moon brings fair weather. ... ...
