| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | when do this [vb infin] | 16 |
|
| 2 | when [vb past] this [vb infin] | 15 |
|
| 3 | when did this [vb infin] | 15 |
|
| 4 | when [verb] this happen | 12 |
|
