| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a [adv] long period of | 11 |
|
| 2 | [prep] a [adv] long period of | 7 |
|
| 3 | for a [adv] long period of | 6 |
|
| 4 | over a [adv] long period of | 5 |
|
