| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | to be [vb pp] [prep] a period | 17 |
|
| 2 | [prep] be [vb pp] [prep] a period | 17 |
|
| 3 | to be [vb pp] [prep] a period | 17 |
|
| 4 | [prep] be [vb pp] over a period | 8 |
|
| 5 | [prep] be [vb pp] within a period | 5 |
|
