| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [be] shown to [be] essential | 5 |
|
| 2 | be shown to [be] essential | 5 |
|
| 3 | shown to [be] essential [prep] | 5 |
|
| 4 | shown to [be] essential [prep] | 5 |
|
