it is......that......？句型的含义

1.It is + 被强调部分 + that ... 就是强调句

该句型是强调句型。将被强调的部分放在前面，其它部分置于that之后。被强调部分可以是主语，宾语，表语或状语。强调的主语如果是人，that可以由who换用。如果把这种句型结构划掉后，应该是一个完整无缺的句子。这也是判断强调句型与其它从句的方法。

It was about 600 years ago that the first clock with a face and an hour hand was made.

It was they that (who ) cleaned the classroom yesterday.

It was in the street that I met her father.

补充：
2. 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。