| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | must have [been] [adv] | 535 |
|
| 2 | must have [been] a | 430 |
|
| 3 | have [been] [adv] a | 373 |
|
| 4 | must have [adv] a | 6 |
|
