| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [vb mod] have been due to | 37 |
|
| 2 | [modal v] have been due to | 37 |
|
| 3 | [modal v] have been due to | 37 |
|
| 4 | may have been due to | 23 |
|
| 5 | may have been due to | 23 |
|
| 6 | might have been due to | 8 |
|
| 7 | might have been due to | 8 |
|
