| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] [num] years ' duration | 56 |
|
| 2 | [prep] [num] years ' duration | 56 |
|
| 3 | of [num] years ' duration | 52 |
|
| 4 | [prep] three years ' duration | 25 |
|
| 5 | [prep] four years ' duration | 19 |
|
| 6 | [prep] two years ' duration | 7 |
|
