| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [num] [noun pl] [prep] the [adj] period | 18 |
|
| 2 | [num] [noun pl] [prep] a [adj] period | 15 |
|
| 3 | [num] [noun pl] over [art] [adj] period | 12 |
|
| 4 | [num] years [prep] [art] [adj] period | 6 |
|
