| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | a once in a [noun] | 10 |
|
| 2 | a once in a [noun] | 10 |
|
| 3 | a once in a [noun sg] | 10 |
|
| 4 | a once in a lifetime | 8 |
|
| 5 | a once in a lifetime | 8 |
|
