| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | must have [be] [v-ing] [pron] for | 6 |
|
| 2 | must [vb infin] been [v-ing] [pron] for | 6 |
|
| 3 | must [vb infin] be [v-ing] [pron] for | 6 |
|
| 4 | must [vb infin] [been] [v-ing] [pron] for | 6 |
|
