| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | at [adv] four years | 18 |
|
| 2 | at [adv] four years | 18 |
|
| 3 | at least four years | 16 |
|
| 4 | at least four years | 16 |
|
| 5 | at [noun] four years | 6 |
|
| 6 | at [noun prp] four years | 5 |
|
