| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [vb past] [be] in operation since | 5 |
|
| 2 | [vb past] be [prep] operation since | 5 |
|
| 3 | had [be] [prep] operation since | 5 |
|
| 4 | [vb past] [been] [prep] operation since | 5 |
|
| 5 | [vb past] been [prep] operation since | 5 |
|
