语法复习五：强调句、It的用法、省略和插入语
一、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 was yesterday that 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 it yesterday that 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 where was 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。
二、It的用法
（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。详见"一、强调句"。
（四）引导词it作形式主语（宾语）
为了使句子平衡，常采用形式主语（或宾语）it ，而把真正的主语（或宾语）置于句子后面。通常引导词it与它所代替的句子成分中间要夹有某些词。
e.g. It takes half an hour to go there on foot.（It与to go there on foot之间夹有takes half an hour四个词）
We thought it strange that Mr Smith did not come last night. （it与that从句中间夹有 strange）
但有时it与所替代部分之间并不夹有其它词。
e.g. You may depend on it that they will support you.（因为介词on之后一般不直接接that引导的宾语从句。注意：it不是多余的，不能当作错句）
练习一、强调句、It的用法
1. My bike is missing. I can't find ____ anywhere.
A. one B. ones C. it D. that
2. ---- Who's that? ---- ____ Professor Li.
A. That's B. It's C. He's D. This's
3. ____ was Jane that I saw in the library this morning.
A. It B. He C. She D. That
4. ---- Have you ever seen a whale alive? ---- Yes, I've seen ____.
A. that B. it C. such D. one
5. The color of my coat is different from ____ of yours.
A. this B. that C. it D. one
6. ____ will do you good to do some exercise every morning.
A. It B. There C. Those D. You
7. We think ____ our duty to pay taxes to our government.
A. that B. this C. its D. it
8. The climate of Shanghai is better than ____ of Nanjing.
A. that B. it C. which D. what
9. ____ four years since I joined the Army.
A. There was B. There is C. It was D. It is
10. How long ____ to finish the work?
A. you'll take B. you'll take it C. will it take you D. will take you
11. It was through Xiao Li ____ I got to know Xiao Wang.
A. who B. whom C. how D. that
12. It was in the rice fields ____ we had our league meeting.
A. where B. that C. in which D. on which
13. It was on October 1st ____ new China was founded.
A. which B. when C. as D. that
14. Was it because he was ill ____ he asked for leave?
A. and B. that C. that's D. so
15. Mary speaks in a low voice; ____ is difficult to know what she is saying.
A. it B. that C. so D. she
16. It was ____ I met Mr Green in Shanghai.
A. many years that B. many years before C. many years ago that D. many years when
17. ____ is not everybody ____ can draw so well.
A. It, all B. It, that C.