| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | must have been [verb] [det] | 17 |
|
| 2 | must have [been] [verb] [det] | 17 |
|
| 3 | must have [been] [v-ing] [det] | 12 |
|
| 4 | must have [been] [verb] all | 5 |
|
