| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a period of years [prep] | 10 |
|
| 2 | [prep] a period of years [prep] | 10 |
|
| 3 | over a period of years [prep] | 8 |
|
| 4 | over a period of years [prep] | 8 |
|
| 5 | a period of [adj] years [prep] | 49 |
|
| 6 | a period of [num] years [prep] | 45 |
|
| 7 | a period of five years [prep] | 9 |
|
| 8 | a period of five years [prep] | 9 |
|
| 9 | a period of three years [prep] | 6 |
|
| 10 | a period of three years [prep] | 6 |
|
| 11 | a period of two years [prep] | 5 |
|
| 12 | a period of two years [prep] | 5 |
|
