语法总结
被动语态的多种时态
was asked、had been found、was picked up、is being sent 分别表达过去被动、过去完成被动和现在进行时被动。
相似句：
- The letter was sent yesterday.
- The parcel is being sent now.
过去完成时
had been found 早于“警察告诉他”这一过去动作。
相似句：
- The bike had been stolen years before.
- The work had been finished by noon.