| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | at [adv] [prep] a | 274 |
|
| 2 | at [adv] once a | 118 |
|
| 3 | at [adv] once [prep] | 53 |
|
| 4 | at once [prep] a | 50 |
|
| 5 | [adv] once [prep] a | 40 |
|
