| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a period of | 1600 |
|
| 2 | [to-vb] [prep] a period | 26 |
|
| 3 | [to-vb] a period of | 26 |
|
| 4 | [to-vb] [prep] period of | 12 |
|
