表语用来说明主语的性质、特征、状态、身份等。请教老师这个性质如何理解? 能否举例说明。

以下划线的表语分表表示性质、特征、状态或身份的哪一种呢？

Life is not a bed of roses. 

This pair of shoes is hers.

To a doctor, the most important thing is to save life.

To see is to believe.

His job is to teach English. 

Time is up.