| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | be [prep] [num] years ' duration | 49 |
|
| 2 | [be] [prep] [num] years ' duration | 49 |
|
| 3 | [is] [prep] [num] years ' duration | 45 |
|
| 4 | is [prep] [num] years ' duration | 45 |
|
