| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [is] necessary [verb] [noun] | 148 |
|
| 2 | [is] often necessary [verb] | 25 |
|
| 3 | [is] often [verb] [noun] | 24 |
|
| 4 | often necessary [verb] [noun] | 10 |
|
