| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | problem have been | 165 |
|
| 2 | problem has been | 134 |
|
| 3 | problems have been | 84 |
|
| 4 | problem have been | 67 |
|
| 5 | problem had been | 41 |
|
| 6 | problem 's been | 6 |
|
