| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [pron] [adv] difficult to maintain | 7 |
|
| 2 | [pron] [adv] difficult maintain | 7 |
|
| 3 | [pron] [adv] difficult maintain | 7 |
|
| 4 | it [adv] difficult maintain | 6 |
|
| 5 | it [adv] difficult maintain | 6 |
|
| 6 | [pers pn] [adv] difficult maintain | 6 |
|
