| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | could [be] [verb] | 15987 |
|
| 2 | could [be] [vb pp] | 15275 |
|
| 3 | [modal v] [be] traced | 314 |
|
| 4 | could [be] traced | 23 |
|
| 5 | could [be] trace | 23 |
|
