| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | why did [pron] [verb] back [prep] | 5 |
|
| 2 | why do [pron] [vb infin] back [prep] | 5 |
|
| 3 | why do [pers pn] [verb] back [prep] | 5 |
|
| 4 | why do [pron] [verb] back [prep] | 5 |
|
