It is expected of sb to do sth句式

It is expected of him to see the play. 为何在动词不定式前不需要for，而用了介词for？盼望专家老师解惑。

该句式的基本结构是：expect sth of sb。其被动式就是sth is expected of sb。如：

Good conduct is expected of students in school.学生在校应当操行好。

You have signally failed to do what was expected of you. 期望你做的事你显然并没做。

They showedcommitment to the job above and beyond what was expected of them.他们的敬业精神超乎大家对他们的期望。

对于被动形式的sth is expected of sb 来讲，假如其中的sth为不定式，则在句首用形式主语it，将不定式移至句末，即为 Itis expected of sb to do sth。如你的句子：

It isexpected of him to see the play.=To see the play is expected of him. 期望他去看看这出戏。