| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | be a period of | 156 |
|
| 2 | [was/were] a period of | 78 |
|
| 3 | was a period of | 65 |
|
| 4 | [is] a period of | 36 |
|
| 5 | is a period of | 30 |
|
| 6 | [be] a period of | 30 |
|
| 7 | be a period of | 30 |
|
| 8 | were a period of | 13 |
|
| 9 | been a period of | 9 |
|
| 10 | [been] a period of | 9 |
|
| 11 | 's a period of | 6 |
|
