| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | period [prep] which [art] [noun pl] | 26 |
|
| 2 | period [prep] which the [noun pl] | 26 |
|
| 3 | period in which [art] [noun pl] | 10 |
|
| 4 | period during which [art] [noun pl] | 6 |
|
