| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | it must be [vb pp] [prep] | 288 |
|
| 2 | but it must be [vb pp] | 96 |
|
| 3 | but must be [vb pp] [prep] | 28 |
|
| 4 | but it must be [prep] | 12 |
|
