| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | is difficult [to-vb] [conj] | 225 |
|
| 2 | is difficult [to-vb] a | 94 |
|
| 3 | is [to-vb] [conj] a | 40 |
|
| 4 | difficult [to-vb] [conj] a | 38 |
|
