文档介绍：it的用法及强调结构
I. 作代词
用作人称代词，代替前文提到过的事物（是同一物）。
My pen is missing. I can't find it anywhere.
I was disappointed with the he met in the park yesterday.
强调时间状语： It was yesterday that he met an old friend in the park.
强调地点状语： It was in the park that he met an old friend yesterday.
2） . 强调句型的基础知识：
强调地点状语不用where，时间状语不用when，方式状语不用how，原因状语不用why，都要用that.
It was for this reason that he left that school. （原因状语）
It was in this way that he solved the problem. （方式状语）
. 也可以是状语从句被强调：
It was only when I reread his poems that I began to appreciate their beauty. （时间状语从句）
It was because she got up late that she didn't catch the first bus. （原因状语从句）
被强调部分如果是原句的主语，who/that后的谓语在人称和数上应和原句的主语一致。
It is Mary who often does good deeds.
. 强调句型可以是个否定句：
It was not I that met your father in the street.
判断一个句子是否是强调句的方法：如果将句中的It is/was...that/who去掉，经整理后还是一个完整的句子，本句就是强调句，否则，就不是。
It was in today's newspaper that we found the news.
We found the news in today's newspaper.（句子意思完整，所以上句是强调句）
强调一般疑问句中的某一个成分时，要用一般疑问句的语序，把is/was提前。
Did this happen in Beijing ?
—Was it in Beijing that this happened ?
Wasn't it he that had made a mistake ?
. 特殊疑问句只有疑问词可以强调：
疑问词+is/was it +that-clause ?
Where were you born ?
—Where was it that you were born ?
强调句型的系动词除了用is/was外，还可以在其前面加上may/might/must等表示推测的情态动词。
It might be him that you met yesterday.
. 在被强调的部分后接定语从句，使句子结构更加复杂。
It was in Beihai Park they made a date for the first time the old couple told us their love story.
A. where, that B. that, that C. where, when D. that, when
，缺地点状语，用where,:It was on July 7也
1975 when he was born that his father died.
not...until...的强调句型：
It is / was not until ＋时间状语＋ that-clause
Not until+时间状语+ （主句的）倒装句
I didn't realize she was a film star until she took off her dark glass.
—It was not until she took off her dark glasses that I realized she was a film star.
—Not until she took off her dark glasses did I realize she was a film star.
注意：此句型只用unti 1,不用till。但如果不是强调句型，til