| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | have been a source [prep] [noun] | 5 |
|
| 2 | have been a source [prep] [noun sg] | 5 |
|
| 3 | [modal v] have been a source [prep] | 6 |
|
| 4 | [vb mod] have been a source [prep] | 6 |
|
