It is + time + clause是英语中一个常用句型，也是高考必须把握的热点和难点，现归纳如下：
一、用在when引导的定语从句中， 其功能相当于一个由并列连词连接的分句
例 It was October the thirty-first when we went to Beijing. =It was October the thirty-first and on that day we went to Beijing.我们是12月31号去的北京。
二、 用在that引导的强调句中。注意时间前介词的应用
