| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | is difficult [to-vb] | 1938 |
|
| 2 | it is difficult | 1916 |
|
| 3 | it is [to-vb] | 1163 |
|
| 4 | it difficult [to-vb] | 1117 |
|
