| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [be] [vb pp] at [adv] once a | 12 |
|
| 2 | be [vb pp] at [adv] once a | 12 |
|
| 3 | [vb pp] at [adv] once a [noun sg] | 19 |
|
| 4 | [vb pp] at [adv] once a [noun] | 19 |
|
| 5 | [vb pp] at [adv] once a week | 9 |
|
| 6 | [vb pp] at [adv] once a week | 9 |
|
| 7 | [vb pp] at [adv] once a year | 7 |
|
| 8 | [vb pp] at [adv] once a year | 7 |
|
