| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | who [vb past] [been] on duty | 6 |
|
| 2 | who [vb past] [been] [prep] duty | 6 |
|
| 3 | who [vb past] [been] on duty | 6 |
|
| 4 | who [vb past] [been] [prep] duty | 6 |
|
| 5 | who [vb past] been [prep] duty | 6 |
|
| 6 | who [vb past] [been] [prep] duty | 6 |
|
| 7 | who had [been] [prep] duty | 5 |
|
