| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | be [verb] over a period of | 15 |
|
| 2 | be [verb] over a period [prep] | 15 |
|
| 3 | be [verb] over a period [prep] | 15 |
|
| 4 | be [vb pp] over a period [prep] | 15 |
|
