| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | system have been [art] [adj] [noun sg] | 9 |
|
| 2 | system have been a [adj] [noun sg] | 9 |
|
| 3 | system have been [art] [adj] [noun sg] | 8 |
|
| 4 | system have been a [adj] [noun sg] | 8 |
|
| 5 | system has been [art] [adj] [noun sg] | 6 |
|
