| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | be [prep] a period of | 23 |
|
| 2 | be [prep] a period of | 23 |
|
| 3 | be in a period of | 9 |
|
| 4 | be for a period of | 9 |
|
| 5 | be in a period of | 9 |
|
| 6 | be for a period of | 9 |
|
| 7 | is [prep] a period of | 6 |
|
| 8 | be [prep] a period of | 6 |
|
