it is time 的用法,

这是英语语法的事,怎么跑到电脑、网络上来了
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It's time…句型是中学英语里使用频率较高的句型,其意为“该是……的时候了”.用法灵活多变,也是大家以掌握的句型.现就其有关句式归纳如下：
⑴ It's time for + n.“该是（干）……的时候了.”例：
Boys and girl,It's time for class.
同学们,该上课了.
⑵ It's time + (for sb.) to do sth..表示“该是（某人）干……的时候了.”例：
It's time for you to clean the classroom.
该是你打扫教室的时候了.
It's time to go to school.
该去上学了.
⑶ It's time + that clause 时,that可省略,time可由high,about修饰,从句中的谓语动词有两种形式,或者用动词的过去式(be用were)；或者用shoud + 动词原形（should不能省略).此句型为虚拟语气句型,表示“现在某人该做某事了”.含有该事早该去做而未做,现在去做似乎都为时已晚的意思.例：
It's time （that）we went to bed.
我们该去睡觉了.
It's high time that the article were published.
发表这篇文章是适时的.
It's time you should do cleaning.
你该去打扫卫生了.
⑷ It's + the/序数词+ time +to do sth.表示某人第几次做某事.例：
It is my first time to write letter in English.
这是我第一次用英语写信.
⑸ It's + the+序数词+ time+ that clause.也 表示某人第几次做某事.例：
It is my first time that I've even written letters.
这是我第一次用写信.
句型⑷ 句型 ⑸ 可以互换.