| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [noun pl] [prep] a long period of | 11 |
|
| 2 | [noun pl] [prep] a long period of | 10 |
|
| 3 | [noun pl] over a long period of | 8 |
|
| 4 | [noun pl] over a long period of | 8 |
|
