| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | at a [noun] | 15341 |
|
| 2 | at a [noun sg] | 14548 |
|
| 3 | [prep] a period | 2137 |
|
| 4 | at [art] period | 34 |
|
| 5 | at [art] period | 34 |
|
| 6 | at a period | 17 |
|
| 7 | at a period | 17 |
|
