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高中英语语法it的用法
高中阶段的英语学习，其实就是学语法、记单词和研究并熟练题型。其中，语法是大多数同学最头疼的问题，原因在于其内容之繁杂和零散，下面是小编收集整理的高中英语语法it的用法，供大家参考借鉴，希望可以帮助到有需要的朋友。
It用法及其句型和固定搭配，是高中英语语法的重点、难点，又是高考英语的热点，因此应给予充分的重视，现将it用法归纳如下：
一、作人称代词
1、it代替前面(或后面)的单数名词或分句等所表示的事物。
e.g. You cannot eat your cake but have it.(it代替前面的cake)Although we cannot see it, there is air all around us. (it代替后面的air)They say he has left town, but I don’t believe it. (it代替前面They…town分句中的情况)
2、代替有生命但不能或不必分阴阳性的东西(包括婴儿)。
e.g. Yesterday we saw a big tree. It was fully twenty metres high. (it代替前面的tree)The baby cried because it was hungry. (it代替前面的baby)
3、在某些习惯说法中，可以代替人。
e.g. -- Someone is knocking at the door, Peter. -- Who is it? -- It’s me.
-- Who are singing? -- It is the children.
-- The light is still on in the lab. It must be the third-year students doing the experiment.
4、it与one的区别：这两个词都可以代表前面说过的名词，但it用于同名同物的场合;one则用于同名异物的场合。
e.g. -- Do you still have the bicycle? -- No, I have sold it.
-- Is this knife yours? -- No. It is Xiao Zhang’s. Mine is the one on the desk.
5、it与that的区别：两词都可代替某一特定名词，但that指同一类，并非同一个。
e.g. The climate of South China is mild(温和的); I like it very much.(it指the climate of South China)The climate of South China is much better than that of Japan.(that指the climate)
二、作无人称代词it作无人称代词时，除了句中找不到它所代表的词语外，另一个特点是它后面的内容都是表示天气、时间、距离、度量衡及情况等。
It is fine (rainy, windy, etc.).
It is noon.
It is a half hour’s walk to the factory.
It is eighteen square metres in area.
What does it matter?
三、作强调词，构成强调结构用以帮助改变句子结构，使句子的某一成分受到强调。
“It is (was) + 所强调的成分+ that (who) + 其它成分。”在这个句型中，it本身没有词义。在使用强调句型时需注意以下几点：
1. 请注意强调句型的特殊疑问句例When was it that he changed his mind to take part in the activity?
2. 在强调原因状语从句时，只能强调由because所引导的从句例It was because he was ill that he didnt come to school yesterday.
3. 在强调not … until结构时必须把not与until一起放到被强调的位置上例It was not until she took off her dark glasses that I realized she was my brother.
4. 注意强调句型与定语从句的区别例It was at 7 oclock that he came here yesterday.( 强调句型)It was 7 oclock when he came here yesterday.(定语从句)四、It用作形式主语It替代作主语的从句、动词不定式、动名词，而把真正作主语的从句、动词不定式、动名词置于句尾
四、强调句
（一）强调句句型
1、陈述句的强调句型：It is/ was +被强调部分（通常是主语、宾语或状语）+ that/ who（当强调主语且主语指人）+ 其它部分。e.g. It wasyesterdaythat he met Li Ping.
2、一般疑问句的强调句型：同上，只是把is/ was提到it前面。e.g. Was ityesterdaythat he met Li Ping?
3、特殊疑问句的强调句型：被强调部分（通常是疑问代词或疑问副词）+ is/ was + it + that/ who +其它部分？e.g.When and wherewas it that you were born?
4、强调句例句：针对I met Li Ming at the railway station yesterday.句子进行强调。强调主语：It was I that (who) met Li Ming at the railway station yesterday.强调宾语：It was Li Ming that I met at the railway station yesterday.强调地点状语：It was at the railway station that I met Li Ming yesterday.强调时间状语：It was yesterday that I met Li Ming at the railway station.
5、注意：构成强调句的it本身没有词义；强调句中的连接词一般只用that, who，即使在强调时间状语和地点状语时也如此，that, who不可省略；强调句中的时态只用两种，一般现在时和一般过去时。原句谓语动词是一般过去时、过去完成时和过去进行时，用It was …，其余的时态用It is …。
（二）not … until …句型的强调句
1、句型为：It is/ was not until +被强调部分+ that +其它部分e.g. 普通句：He didn’t go to bed until/ till his wife came back.强调句：It was not until his wife came back that he went to bed.
2、注意：此句型只用until，不用till。但如果不是强调句型，till, until可通用；因为句型中It is/ was not …已经是否定句了，that后面的从句要用肯定句，切勿再用否定句了。
（三）谓语动词的强调
1、It is/ was … that …结构不能强调谓语，如果需要强调谓语时，用助动词do/ does或did。e.g. Do sit down. 务必请坐。He did write to you last week. 上周他确实给你写了信。Do be careful when you cross the street. 过马路时，务必（千万）要小心啊！
2、注意：此种强调只用do/ does和did ，没有别的形式；过去时用did ，后面的谓语动词用原形。
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