如何区分it is 是强调句还是形式主语

1、强调句的用法

1.强调句it is not +连词

It was not until his wife came back that he went to bed.

直到他的妻子返回，他才去睡觉。

2.强调句it  was+时间状语

It was last night that his mother worked at factory

正是昨晚，他的母亲在工厂里工作。

3.强调句it is +宾语（或者人）

It is Li Lei’s brother that you met in the street yesterday. 

你昨天在街上所见到的就是李雷的兄弟

4.it is+接地点状语

it is street that you met lilei's brother yesterday 

你昨天在街上遇见的是李磊的兄弟

5.it is +名词（人）

it is this man who gave me the food

给我食物的是这个男人.

6.it is+宾语(人)

 it is this man whom I met in the street

我在街上遇到的是这个男人.

强调句通常是it is 接名词(人).状语.宾语.连词表示强调句

2、形式主语的句子

1.it is+形容词

it is diffcult to do the work。

做这个工作是非常困难的。

it做形式主语。

2.it is+形容词+that

it is surprise that you give me the gift

你给我这个礼物是非常惊讶的。

3.it is+名词

it is an honor that president give me the gift

总统给我这个礼物是一个荣幸.

4.it +不及物动词 +that

it seems that this thing is true

似乎这个事情是真的.

5.it is接过去分词

it is said that the pirates buried  the treasure in the ground

据说，海盗绑宝藏在这个洞里.

形式主语通常接接名词 形容词 不及物动词 过去分词