| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [coord] once [prep] a [noun] | 12 |
|
| 2 | [coord] once [prep] a [noun sg] | 12 |
|
| 3 | [coord] once [prep] a while | 5 |
|
| 4 | [coord] once [prep] a while | 5 |
|
