| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | must [vb infin] [be] [adj] | 772 |
|
| 2 | must [vb infin] [be] [adj] | 556 |
|
| 3 | [modal v] [vb infin] [be] difficult | 75 |
|
| 4 | must [verb] [be] difficult | 12 |
|
| 5 | must [vb infin] [be] difficult | 12 |
|
