| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | could [vb infin] [pron] have happened | 10 |
|
| 2 | could [vb infin] [pron] have happen | 10 |
|
| 3 | could [vb infin] [pron] had happen | 9 |
|
| 4 | could [vb infin] what have happen | 8 |
|
| 5 | could [vb infin] what have happen | 8 |
|
| 6 | could [vb infin] [Wh det] have happen | 8 |
|
| 7 | could see [pron] have happen | 5 |
|
