嗯,可以这么说……
其实The work done by the man was difficult可以变成从句形式：
The work which was done by the man was difficult.
（which was） done by the man是后置定语,修饰前面的the work,
字面上翻译是“被那个人做了的事情”,变为主动也就是“那个人做了事情”