| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [num] years ['s] duration | 70 |
|
| 2 | [num] years ' duration | 70 |
|
| 3 | [num] years ' duration | 70 |
|
| 4 | [num] years [unc] duration | 70 |
|
| 5 | four years [unc] duration | 27 |
|
| 6 | three years [unc] duration | 25 |
|
| 7 | two years [unc] duration | 7 |
|
