| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [vb pp] [prep] a long period [prep] | 28 |
|
| 2 | [vb pp] [prep] a long period of | 27 |
|
| 3 | [vb pp] over a long period [prep] | 16 |
|
| 4 | [vb pp] for a long period [prep] | 7 |
|
