| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | must have been about | 10 |
|
| 2 | must have [be] about | 10 |
|
| 3 | must have be about | 10 |
|
| 4 | must have [been] about | 10 |
|
| 5 | must have [be] about | 9 |
|
