| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | how could it have [vb pp] | 10 |
|
| 2 | [Wh adv] could it have [vb pp] | 10 |
|
| 3 | how could it have [vb pp] | 10 |
|
| 4 | [adv] could it have happened | 5 |
|
