[观察例句]
1．All the work has been finished by now.
2．Now she was being looked after by a robot that looked so human，and it was disturbing.
3．Some words and phrases are often used to compare and contrast information.
[归纳用法]
1．例句1中的黑体词部分为现在完成时的被动形式，表示到现在为止已完成的被动动作。
2．例句2中的黑体词部分为过去进行时的被动形式，表示在过去某个时候正在进行的被动动作。
3．例句3中的黑体词部分为一般现在时的被动形式，表示经常性的被动动作。
