| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a three year period | 17 |
|
| 2 | [prep] a three year period | 17 |
|
| 3 | [prep] a three year period | 17 |
|
| 4 | over a three year period | 11 |
|
| 5 | over a three year period | 11 |
|
