| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a fixed period [prep] time | 16 |
|
| 2 | [prep] a fixed period [prep] time | 16 |
|
| 3 | for a fixed period [prep] time | 11 |
|
| 4 | for a fixed period [prep] time | 11 |
|
