| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | could [adv] have been long | 5 |
|
| 2 | could [adv] have [been] long | 5 |
|
| 3 | could not have [been] long | 5 |
|
| 4 | could [not/n't] have [been] long | 5 |
|
