| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | systems have been | 89 |
|
| 2 | systems have [been] | 89 |
|
| 3 | systems have be | 89 |
|
| 4 | systems have [be] | 61 |
|
| 5 | systems has [be] | 21 |
|
| 6 | systems had [be] | 7 |
|
