| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [vb past] [prep] a | 32941 |
|
| 2 | once [prep] a | 498 |
|
| 3 | [vb past] once [prep] | 70 |
|
| 4 | [vb past] once a | 24 |
|
