| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [verb] [prep] a period of | 372 |
|
| 2 | [prep] a long period of | 152 |
|
| 3 | [verb] [prep] a long period | 91 |
|
| 4 | [verb] a long period of | 16 |
|
