| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | it [vb past] been [adj] | 493 |
|
| 2 | it [verb] been necessary | 45 |
|
| 3 | [pron] [vb past] been necessary | 16 |
|
| 4 | it [vb past] be necessary | 13 |
|
| 5 | it [vb past] [been] necessary | 13 |
|
| 6 | it [vb past] [be] necessary | 13 |
|
