| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | for a certain period [prep] [noun] | 8 |
|
| 2 | for a certain period [prep] time | 7 |
|
| 3 | for a certain period [prep] [noun sg] | 7 |
|
| 4 | for a certain period [prep] time | 7 |
|
