| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a [adj] period [prep] | 871 |
|
| 2 | a [adj] period [prep] time | 357 |
|
| 3 | [prep] a period [prep] time | 240 |
|
| 4 | [prep] [adj] period [prep] time | 180 |
|
