| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a [adv] [adj] period [prep] | 81 |
|
| 2 | [prep] a [adv] long [noun] [prep] | 39 |
|
| 3 | [prep] [art] [adv] long period [prep] | 13 |
|
| 4 | [prep] a [adv] long period [prep] | 13 |
|
