| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | it must [vb infin] been [det] [noun] | 19 |
|
| 2 | it must have been [det] [noun] | 19 |
|
| 3 | it must have been [det] [noun] | 18 |
|
| 4 | it must [verb] been [det] [noun sg] | 14 |
|
| 5 | it must [verb] been some [noun] | 12 |
|
| 6 | it must [verb] been [det] [noun pl] | 5 |
|
