| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | be operate for | 30 |
|
| 2 | [be] operating for | 22 |
|
| 3 | been operate for | 18 |
|
| 4 | [been] operate for | 18 |
|
| 5 | [be] operated for | 7 |
|
