| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | it must [prep] be | 50 |
|
| 2 | it must [prep] [be] | 50 |
|
| 3 | it must [prep] been | 50 |
|
| 4 | it must [prep] [been] | 50 |
|
| 5 | it must of [be] | 50 |
|
