| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | must have [been] [v-ing] [prep] | 81 |
|
| 2 | [modal v] have [been] [v-ing] for | 55 |
|
| 3 | must have [been] [verb] for | 36 |
|
| 4 | must have [be] [v-ing] for | 18 |
|
| 5 | must [verb] [been] [v-ing] for | 18 |
|
