| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | be [v-ing] [prep] happen when | 7 |
|
| 2 | [be] [v-ing] [prep] happen when | 7 |
|
| 3 | 's [v-ing] [prep] happen when | 6 |
|
| 4 | [is] [v-ing] [prep] happen when | 6 |
|
| 5 | [v-ing] [prep] happen when [pers pn] | 6 |
|
| 6 | [v-ing] [prep] happen when [pron] | 6 |
|
