| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [pron] [modal v] [be] difficult [to-vb] | 398 |
|
| 2 | [Wh det] [modal v] [be] [adj] [to-vb] | 150 |
|
| 3 | [Wh det] [modal v] [be] difficult [to-vb] | 37 |
|
| 4 | [Wh det] [modal v] [be] difficult [verb] | 37 |
|
