| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a [adj] period | 1646 |
|
| 2 | [prep] a period of | 1599 |
|
| 3 | a [adj] period of | 781 |
|
| 4 | [prep] a [adj] of | 42 |
|
