| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | difficult [to-vb] in [noun sg] | 60 |
|
| 2 | difficult [to-vb] in [noun sg] | 60 |
|
| 3 | difficult [to-vb] in practice | 22 |
|
| 4 | difficult to keep in [noun sg] | 6 |
|
| 5 | difficult to achieve in [noun sg] | 6 |
|
| 6 | difficult to apply in [noun sg] | 5 |
|
