| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | difficult [verb] | 9698 |
|
| 2 | difficult [to-vb] | 9625 |
|
| 3 | [adj] to keep | 1541 |
|
| 4 | [adj] to keep | 1286 |
|
| 5 | difficult keep | 117 |
|
| 6 | difficult to keep | 116 |
|
