当需要强调句中的主语、宾语、状语时，我们常用“It is/was+被强调部分+that/who...”这样的句型，被强调的部分放在前面，其它部分置于that之后。强调的主语如果是人，that可以换用who。如何区分这种强调句句型与that从句？如果把这种句型中的句型结构部分(It is/was...that/who...)划掉后，是一个完整无缺的句子即是强调句。
He read three books in the library yesterday.
我们分别可以强调主语、宾语、地点状语和时间状语。如：
It was he who(that)read three books in the library yesterday.(强调主语)
It was three books that he read in the library yesterday.(强调宾语)
It was in the library that he read three books yesterday.(强调地点状语)
It was yesterday that he read three books in the library.(强调时间状语)
在使用It is/was...that/who...强调句型时应注意以下几点：
1、当被强调部分指人时，可用that，也可以用who;指物时，只能用that,如：
It was Tom who(that)I met last week.我上周遇见的就是汤姆。
It is a new boke that his brother wants to buy.他的弟弟就想买一个新博客。
2、强调状语时，只有that,不用when、where，如：
It is at 5 o'clock that the train will arrive. 五点钟是火车到达的时间。
3、被强调的部分是主语时，注意主谓语动词和被强调的主语保持一致，如：
It is he who is late. 是他迟到了。
It is they that were late.是他们迟到了。
4、一般疑问句的强调句为“Is (was) it + that...?”；特殊疑问句为：“特殊疑问词+ is (was) +that...?”结构。如:
Was it ten years ago that his father died?（他的父亲是十年前去世的吗？）
When is it that you will set off?（你到底什么时候出发？）
It is/was...that/who...强调句型扩展讲解
1、It is not until + 被强调部分 + that ...
该句型也是强调句型。主要用于强凋时间状语，译成汉语”直到...才..”，可以说是 not ... until ... 的强调形式。
It was not until she took off her dark glasses that I realized she was a famous film star.
= Not until she took off her dark glasses did I realize she was a famous film star.
= I didn’t realize she was a famous film star until she took off her dark glasses.
3. It is clear ( obvious, true, possible, certain....) that .....
该句型中it 是形式主语，真正的主语是that 引导的主语从句，常译为”清楚（显然，真的，肯定．．．）” 是主语从句最常见的一种结构。
It is very clear that he’s round and tall like a tree.
= That he’s round and tall like a tree is very clear.
4. It is important ( necessary, right, strange, natural...) that ...
该句型和上一个同属一个句型。由于主句中的形容词不同，that 后的从句中要用虚拟语气（should + 动词原形），should 可以省去。建议记住该句型中的形容词。
It is important that we (should) learn English well.
It is necessary that he (should) remember these words.
5. It is said (reported, learned....) that ...
该句型中的it 仍是形式主语，真正主语是that 引导的主语从句。该结构常译为”据说（据报道，据悉．．．）”。
It is said that he has come to Beijing.
It is reported that another earth satellite has been put into orbit.
6. It is suggested ( ordered ... ) that ...
该句型和上一个同属一个句型。主句中的过去分词是表示请求，建议，命令等词时，that 后的从句要用虚拟语气（should + 动词原形），should 可以省。常译为”据建议；有命令．．．）
It is suggested that the meeting ( should ) be put off.
It was ordered that we ( should ) arrive there in two hours.
7. It is a pity ( a shame ... ) that ...
该句型中，that后的从句一般用虚拟语气（should + 动词原形），should可省去．表示出乎意料，常译为”竟然”。没有这种意义时，则不用虚拟语气。
It is a pity that such a thing ( should ) happen in your class.
这种事竟然发生在你们班上，真是遗憾！
It is a pity that he is ill. 他生病了，真遗憾！
8. It is time ( about time ,high time ) that ...
该句型中that 后的从句应该用虚拟语气，值得注意的是① 常用过去时态表示虚拟．② 有时也用should + 动词原形，should 不能省。常译为”是（正是）．．．的时侯．．．”。
It is time that children should go to bed.
= It is time that children went to bed.
9. It is the first ( second ... ) time that ...
该句型要和上一个句型区别开来。该句型中的 that 从句不用虚拟语气，而用完成时态。
至于用什么完成时态，由主句的谓语动词的时态决定。如果是一般现在时，后面从句用现在完成时态；如果是一般过去时，后面从句则用过去完成时态。该结构中 that 可以省去；it有时用 this 替换．常译为”是第一（二）．．．次．．．”。
It is the first time I have been here.
= This is the first time I have been here.