| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | be [vb pp] [prep] a period of | 50 |
|
| 2 | be [vb pp] over a period of | 15 |
|
| 3 | be [vb pp] for a period of | 11 |
|
| 4 | be [vb pp] within a period of | 10 |
|
| 5 | be [vb pp] as a period of | 5 |
|
