| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [vb pp] [prep] a | 114257 |
|
| 2 | once [prep] a | 498 |
|
| 3 | [vb pp] once [prep] | 107 |
|
| 4 | [vb pp] once a | 68 |
|
