| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a [adj] period of | 544 |
|
| 2 | [prep] a period of [noun pl] | 123 |
|
| 3 | [prep] a [adj] of [noun pl] | 22 |
|
| 4 | a [adj] period of [noun pl] | 14 |
|
