强调句的有关知识
1.定义：强调句型是通过it强调词来改变句子结构，使句子的某一成分受到强调而构成的强调结构
2、基本结构:
(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。强调句可以强调除谓语以外的一切成分。下面我们针对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.
(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 my old friend?
(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 was it that you were born?
我们需要注意的是：第一、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。
第二、It's ....that/who....的强调句型只是为了强调某一成分，而不充当成分。所以它和It作形式主语，真正的主语从句后置的情况有所不同。
我们一起看下面两个例句:
1.It's necessary that we should learn English.(主语从句)
2.It's not until he got off the bus that he realized his money was stolen.(强调句型)
解析：因为强调句型中的It's....that/who....在句子中不充当任何成分。所以去掉后句子依然完整。
例子2去掉It's....that/who....后就成了
until he got off the bus he realized his money was stolen. 而例子1去掉后句子则不完整。
(4) 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 son came back.
强调句：It was not until his son 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。
备注：同学们在平时的学习和复习中一定要注意辨析强调句型与定语从句、主语从句、状语从句的异同。
3. 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。
参考资料：借用的