| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] 15 [unc] | 324 |
|
| 2 | [prep] 15 years | 284 |
|
| 3 | [prep] years [unc] | 36 |
|
| 4 | 15 years [unc] | 30 |
|
