| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | must [verb] been [prep] | 294 |
|
| 2 | must [verb] been [v-ing] | 289 |
|
| 3 | [verb] been [prep] [v-ing] | 144 |
|
| 4 | must [verb] [prep] [v-ing] | 110 |
|
