| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [verb] once [prep] a | 45 |
|
| 2 | [verb] once in a | 20 |
|
| 3 | [vb pp] once [prep] a | 17 |
|
| 4 | [vb past] once [prep] a | 13 |
|
| 5 | [vb base] once [prep] a | 6 |
|
| 6 | [verb] once on a | 6 |
|
| 7 | happen once [prep] a | 5 |
|
| 8 | [verb] once upon a | 5 |
|
| 9 | [vb -s] once [prep] a | 5 |
|
