| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | it be [adv] difficult [to-vb] whether | 25 |
|
| 2 | it is [adv] difficult [verb] whether | 18 |
|
| 3 | it be [adv] difficult to know whether | 8 |
|
| 4 | it be [adv] difficult know whether | 8 |
|
| 5 | it be sometimes difficult [verb] whether | 5 |
|
| 6 | it be often difficult [verb] whether | 5 |
|
