| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [verb] a long period [prep] | 19 |
|
| 2 | [verb] a long period of | 11 |
|
| 3 | [vb pp] a long period [prep] | 7 |
|
| 4 | [vb past] a long period [prep] | 6 |
|
| 5 | have a long period [prep] | 5 |
|
