| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [vb past] [verb] at once | 40 |
|
| 2 | [vb past] [vb pp] [prep] once | 26 |
|
| 3 | had [verb] [prep] once | 23 |
|
| 4 | [vb past] [to-vb] [prep] once | 11 |
|
| 5 | [vb past] [v-ing] [prep] once | 7 |
|
| 6 | [vb past] happen [prep] once | 5 |
|
| 7 | seemed [verb] [prep] once | 5 |
|
