| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a certain period [prep] | 22 |
|
| 2 | [prep] a certain period [prep] | 22 |
|
| 3 | for a certain period [prep] | 9 |
|
| 4 | for a certain period [prep] | 9 |
|
| 5 | a certain period [prep] [noun] | 23 |
|
| 6 | a certain period [prep] [noun sg] | 22 |
|
| 7 | a certain period [prep] time | 19 |
|
| 8 | a certain period [prep] time | 19 |
|
