| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | had operate [prep] | 34 |
|
| 2 | had operated [prep] | 29 |
|
| 3 | had operate in | 13 |
|
| 4 | had operate in | 13 |
|
| 5 | had to operate [prep] | 5 |
|
