| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | gradually [prep] a period [prep] | 7 |
|
| 2 | gradually [prep] a period of | 7 |
|
| 3 | gradually [prep] a period [prep] | 7 |
|
| 4 | gradually [prep] a period of | 7 |
|
