| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | they must have been [verb] [prep] | 20 |
|
| 2 | they must have been [vb pp] [prep] | 14 |
|
| 3 | they must have been [v-ing] [prep] | 6 |
|
| 4 | they must have been [prep] [art] | 5 |
|
| 5 | they must have been [prep] [art] | 5 |
|
