| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a [adj] period of | 514 |
|
| 2 | [vb past] [prep] a period of | 43 |
|
| 3 | [vb past] a [adj] period of | 32 |
|
| 4 | [vb past] [prep] a [adj] period | 27 |
|
