| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | which have been [verb] on a | 12 |
|
| 2 | which [verb] been [vb pp] on a | 12 |
|
| 3 | which [vb past] been [verb] on a | 6 |
|
| 4 | which had been [verb] on a | 6 |
|
