It is(was)加被强调部分加that(who)加句子其他部分是强调句的句型结构。此结构强调的成分仅限于主语，宾语和状语。强调句的连词只有两个，即that和who。强调句是英语的概念，而英语已经发展了1400多年。英语的最早形式是由盎格鲁-撒克逊人移民于5世纪带到英国的一组西日耳曼语支（Ingvaeonic）方言，被统称为古英语。

原句：My father did the experiment in the lab yesterdayevening.

强调主语：Itwas my father who did the experiment in the lab yesterday evening.

强调宾语：Itwas the experiment that my father did in the lab yesterday evening.

强调时间：Itwas yesterday evening that my father did the experiment in the lab.(注意不用when)。