| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a prolonged period [prep] time | 9 |
|
| 2 | [prep] a prolonged period [prep] time | 9 |
|
| 3 | over a prolonged period [prep] time | 7 |
|
| 4 | over a prolonged period [prep] time | 7 |
|
