| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [adv] did it happen | 58 |
|
| 2 | [Wh adv] did it happen | 57 |
|
| 3 | when did it [verb] | 26 |
|
| 4 | when [verb] it happen | 15 |
|
| 5 | when do it happen | 15 |
|
| 6 | when [vb past] it happen | 11 |
|
| 7 | when did [pron] happen | 11 |
|
| 8 | when did it happen | 11 |
|
