| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | a [adj] period of [noun] | 579 |
|
| 2 | over a period of [noun] | 296 |
|
| 3 | over a [adj] period of | 137 |
|
| 4 | over [adj] period of [noun] | 7 |
|
