| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | problems which [vb mod] be | 28 |
|
| 2 | problems which [vb mod] [be] | 28 |
|
| 3 | problems which [vb mod] be | 28 |
|
| 4 | problems which can [be] | 9 |
|
| 5 | problems which could [be] | 5 |
|
| 6 | problems which must [be] | 5 |
|
