be 用于掌管“时态”，done 描述“被动”，所以be变done不变。
| 时间 | 一般状态 | 进行状态 | 完成状态 |
|---|---|---|---|
| 现在 | am/is/are + done | am/is/are + being done | has/have + been done |
| 过去 | was/were + done | was/were + being done | had + been done |
| 将来 | shall/will + be done |
- He has been invited twice. 他已经被邀请了两次了。
- The housework will be finished by him soon.家务很快就被他做完了。
- The ground has been covered with heavy snow. 地面己经被大雪覆盖了。
- The building will be built soon. 这座大楼马上就要建成了。