| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | must [adv] have [been] a [noun sg] | 9 |
|
| 2 | must [adv] [vb infin] [been] a [noun sg] | 9 |
|
| 3 | must [adv] [vb infin] been a [noun sg] | 9 |
|
