| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a period of | 1599 |
|
| 2 | [conj] a period of | 82 |
|
| 3 | [conj] [prep] a period | 76 |
|
| 4 | [conj] [prep] period of | 23 |
|
