| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a [adj] period [prep] | 773 |
|
| 2 | [prep] a [adj] year period | 110 |
|
| 3 | [prep] a [adj] year [prep] | 68 |
|
| 4 | a [adj] year period [prep] | 26 |
|
