| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a period [prep] time | 239 |
|
| 2 | [prep] a period of time | 239 |
|
| 3 | over a period [prep] time | 184 |
|
| 4 | for a period [prep] time | 33 |
|
| 5 | after a period [prep] time | 10 |
|
