| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [adv] difficult [to-vb] [prep] | 560 |
|
| 2 | [adv] difficult [to-vb] [prep] | 560 |
|
| 3 | [adv] [adj] [to-vb] at | 331 |
|
| 4 | [adv] difficult [verb] at | 29 |
|
| 5 | [adv] difficult [to-vb] at | 28 |
|
