It的用法
一．代替上文中提到过的人或事物。指代人时，一般用于小孩或身份不十分明朗的人。
Eg. 1) －Who is the baby? －It?s my teacher?s son．
2) －Who is that gentleman?
－It's my friend Tom．He(不可用It) wants to see you．
二．用于表达天气、环境、时间、距离、季节等。例如：
1) It?s half an hour?s walk from here to our school．
2) It?s nice and warm here．
3) But it's two o'clock now, and it's time for us to go to school．
三．用作形式主语.
it 没有具体意义，而只是帮助把真正的主语移至句子后尾，使句子显得平稳一些，能借it 给移至句子后尾的主语有三种：一种由不定式表示，一种由动名词表示，一种由从句表示。
1).It 替代真正的主语——动词不定式短语.
It is easier to say than to do .
It is a good act to help the others.
2).it 替代真正的主语——动名词短语,以动名词短语做主语的句子，主要在以no good, no use, no harm, dangerous, foolish 等词作表语的句中.
It?s no harm drinking running water in that area。
It?s foolish talking like that.
3).it 替代从句作主语，用从句做主语的带it 的句子很多,常见的有下面几类： ① It is a pity (a shame ,a fact ,a wonder ,a good thing, etc. ) that?
It is a shame that he didn?t pass the exam.
② It is strange ( surprising, obvious ,true, good, possible, clear, etc. ) that? 。 It was clear that they had no desire for peace.
③ It seems (happened ,turned out, etc.)that?
It seemed that things were not as they expected.
④ It is said( decided ,expected ,etc)that ?
It is said that the tickets have been sold out .
四. 用作形式宾语。
当复合宾语中的宾语是不定式,－ing短语或从句往往用it作形式宾语,而将真正的宾语移至句末,句子重心后移。
1) We find it difficult to learn English well in such a short time．
2) We think it no use crying over spilt milk．
3) We made it clear when and where we were going to have the meeting．
五．用于强调句型，即“It is/was＋被强调部分＋that/who/whom+其它”句型之中。 使用该句型有以下几点请注意：
① 强调句的谓语is或was永远用单数.
It was yesterday that I met your father in the street．
②不管被强调部分是哪种状语，只能用that连接，不得使用where、when等连词. It was in the street that I met your father yesterday．
③被强调部分为人时，可用who(主格或宾格)和whom(宾格)代替that，用that也行。
1) It was your father that/whom /who I met in the street yesterday．
2) It was I that/who met your father in the street yesterday．
④强调句中 也要注意主谓一致、人称一致和否定转移的问题。
1) It is they who are our friends．
2) It was not until ten o'clock that we got home last night．
⑤注意不要混淆强调句和其他从句。It is was?that?为强调句标志，去掉后仍可组成一个完整的句子，只是没被强调,而其他从句一般不具备这一特征。 比较：
1) It was ten o'clock when we got home last night．我们昨晚到家时已十点了。
2) It was at ten o'clock that we got home last night．我们昨晚是在十点到家的。 第一句不是强调句，when不可改为that,因为去掉it was和that后，只能组成“We got home ten o'clock last night．”这样一个不完整的句子；第二句是强调句，that不可改为when．
六．用于特殊句型
在动词like, dislike, hate, appreciate, see to（务必，确保）等后加it，然后再加一个从句。此时，it没有具体意思。例如：
I hate it when someone speaks with a mouthful(满口，满嘴)of food. 我讨厌别人满口食物讲话。
I’ll appreciate it if you can come to my party with your wife. 如果你能和你的妻子一起参加我的聚会，我将感激不尽。
You will see to it that your methods are ideal(理想的)。 你要确保你的方法是最理想的。
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