| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | necessary at [art] | 20 |
|
| 2 | necessary at the | 15 |
|
| 3 | necessary at the | 15 |
|
| 4 | necessary at a | 5 |
|
| 5 | necessary at a | 5 |
|
