| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | could [not/n't] have [vb pp] | 1018 |
|
| 2 | could have [vb pp] a | 273 |
|
| 3 | [not/n't] have [vb pp] a | 231 |
|
| 4 | could [not/n't] have a | 37 |
|
