应该是 What fun it is to do something ! 这是个感叹句 。 it 是形式主语, to do sth 是真正的主语 It is fun to do sth 变为感叹句就是 What fun it is to do something !
!,it作形式主语,更上一层楼。祝您学习进步itisfuntodosth对动词不定式作真正的主语
doing sth