| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | difficult [to-vb] [pron] [is] | 26 |
|
| 2 | [adj] [to-vb] [Wh pn] [is] | 17 |
|
| 3 | difficult [to-vb] [Wh pn] [be] | 12 |
|
| 4 | difficult [verb] [Wh pn] [is] | 6 |
|
