| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | could [vb infin] [been] used | 48 |
|
| 2 | could have [been] used | 48 |
|
| 3 | could [verb] been used | 48 |
|
| 4 | could have [been] used | 48 |
|
| 5 | could [verb] [been] used | 48 |
|
