| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [vb pp] [prep] a period of | 215 |
|
| 2 | [prep] a long period of | 152 |
|
| 3 | [vb pp] [prep] a long period | 67 |
|
| 4 | [vb pp] a long period of | 5 |
|
