it is/was ...that...句型的意思，用法

1。强调结构：It is/was ... that ....
例句：It was at 10 o'clock that I heard the news.

2。表示时间（非强调结构）
例如：It was 10 o'clock when I heard the news.

3。表示“现在离（某事发生）已经有（一段时间）了。”
/“那时离（。。发生）已经有（一段时间）了。”
It is (some time) since .... = It has been (some time) since ....
It was (some time) before ....= It had been (some time) before....
例如：It is 8 years since China joined WTO.

强调句型。