It is ...that这个句型是做强调句的.翻译成“正（就）是玛丽.” ,可以用this is Mary,或that is mary,但没有强调意味,翻译“这是玛丽,”或“那是玛丽”.另外一种情况是,也许你们远远的没有看清楚是男是女,就用it.而后面,如果你要用的话,可以说it is Mary and Peter that.强调“正是玛丽和皮特做了." 还有例子是It is dogs that help people.