| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [adv] difficult to maintain | 26 |
|
| 2 | [adv] difficult to maintain | 26 |
|
| 3 | [be] difficult to maintain | 24 |
|
| 4 | be difficult to maintain | 24 |
|
| 5 | [pers pn] difficult to maintain | 17 |
|
| 6 | [pron] difficult to maintain | 17 |
|
| 7 | it difficult to maintain | 17 |
|
| 8 | it difficult to maintain | 17 |
|
| 9 | is difficult to maintain | 12 |
|
| 10 | [is] difficult to maintain | 12 |
|
| 11 | increasingly difficult to maintain | 9 |
|
| 12 | increasingly difficult to maintain | 9 |
|
| 13 | more difficult to maintain | 6 |
|
| 14 | very difficult to maintain | 6 |
|
| 15 | more difficult to maintain | 6 |
|
| 16 | very difficult to maintain | 6 |
|
| 17 | [was/were] difficult to maintain | 5 |
|
| 18 | be difficult to maintain | 5 |
|
| 19 | [be] difficult to maintain | 5 |
|
| 20 | difficult to maintain [art] | 21 |
|
| 21 | difficult to maintain [art] | 21 |
|
| 22 | difficult to maintain a | 11 |
|
| 23 | difficult to maintain the | 10 |
|
| 24 | difficult to maintain the | 10 |
|
| 25 | difficult to maintain a | 9 |
|
| 26 | difficult to maintain [conj] | 9 |
|
| 27 | difficult to maintain [adj] | 8 |
|
| 28 | difficult to maintain [noun] | 6 |
|
| 29 | difficult to maintain [prep] | 5 |
|
| 30 | difficult to maintain [prep] | 5 |
|
