it作形式主语

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“it”作形式主语

“it”作为形式主语，主要用于使句子平衡，避免英语句子出现头重脚轻，也就是真正的主语部分过分复杂庞大的问题。“it”主要在以下三种情况下作真正主语：

一、不定式为真正主语时：

1. It is/ was+ adj.部分+ to do sth.

Eg. It is necessary to finish the work before leaving for a holiday. **经常谈论“it is+ adj. for sb to do sth.”或者“it is+ adj. of sb to do sth.”的问题。形容词后用of或者用for与形容词所形容的对象有关。 我在非谓语动词不定式部分已经讲过，如形容词形容的是sb,则用of；反之 如果形容词形容的是to do sth，则用for。所以刚才的例句可以变为： It is necessary for the manager to finish the work before leaving for a holiday.

2. It is/ was+ n.部分+ to do sth.

Eg. It is a great pleasure to meet friends from afar.

3. It+ v.部分+ to do sth. 注意，动词不定式作真正主语时，并不是谓语部分只出现be动词，也会出现一些动词，常用的有：take, cost, need, require, make, sound, occur等等。

Eg. 1>. It takes me 20 minutes to walk from my house to school. 2>. It sounds great to make a trip there.

3>. It cost them almost 1 million to buy that cottage.

二、动名词作真正主语时：

1. It is/ was+ adj.部分+ doing sth.

注意在非谓语动词的动名词部分已经提过用于此情况（后跟动名词）的形容词相对固定，有good, useless, foolish, hard, enjoyable, worthwhile和nice。 个别形容词如“nice”后既可跟不定式又可跟动名词，则跟动名词的情况多表示该动作已完成或即将完成。

2. It is/ was+ n.部分+ doing sth.

后跟动名词的名词常有：use, good, fun, a waste of sth., job, task等。 Eg. 1>. It’s no use apologizing to me.

2>. It’s a good job working in the library.

三、名词性从句作真正主语（主语从句，同位语从句，表语从句） 1. It is/ was+ adj.部分+从句

此处的形容词常有certain, obvious, wonderful, true, strange, natural, possible, likely等。 Eg. It’s obvious that you have made a very good impression on the teacher.


2. It is/ was+ n.部分+从句

此处常用动词包括a surprise, an hour, a pity, a fact等等。 It was a pity that you lost the game! 3.It is/ was+ v.部分+从句

此处常用的动词包括seem, happen, appear, look, matter, make, occur(猛然想起)

Eg. It doesn’t matter whether the cat is black or white as long as it catches the mice.

这句话中，真正的主语为划线部分。但是如果将它置于句首，则主语部分太长，因此用it代替放在谓语部分doesn’t前。类似的还有：

It made this father happy that his daughter could read well.

It seems that you don’t enjoy your job. 4. It is/ was+分词+从句

此处常用的分词有said, believed, reported, known, proved, decided, expected, puzzling, surprising, amusing等等。 Eg. It’s reported that they have divorced. It’s puzzling how they solved this problem,

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