| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [be] [vb pp] [prep] a long period | 14 |
|
| 2 | be [verb] [prep] a long period | 14 |
|
| 3 | [be] [verb] over a long period | 10 |
|
| 4 | [be] [verb] [prep] a longer period | 10 |
|
