| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | a period of [noun] [art] | 17 |
|
| 2 | a period of [noun sg] [art] | 15 |
|
| 3 | a period of [noun] the | 14 |
|
| 4 | a period of time [art] | 8 |
|
| 5 | a period of time [art] | 8 |
|
