it is/was ... that 是强调句, 可以强调除了表语以外的其他句子成分 比如
I met Li Ming at the railway station yesterday.
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.
强调原因状语 It is because he is ill that he can’t come.
强调宾语补足语 It was chairman that they elected him.
