这个是强调句型.
It is +sth/adj +that.
由该句型中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.It is urgent that the acte problem of air pollution in the city be solved 是强调urgent
所以吗,that 后的从句中要用虚拟语气（should + 动词原形）,should 可以省去.建议记住该句型中的形容词.其它例句It is important that we (should) learn English well.
下面我们针对I met Li Ming at the railway station yesterday.句子进行强调.强调主语：It was I that (who) met Li Ming at the railway station yesterday.强调宾语：It was Li Ming that I met at the railway station yesterday.强调地点状语：It was at the railway station that I met Li Ming yesterday.强调时间状语：It was yesterday that I met Li Ming at the railway station.
祝好!