| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | a long period [prep] | 245 |
|
| 2 | a long period [prep] | 216 |
|
| 3 | a long period of | 205 |
|
| 4 | a longer period [prep] | 29 |
|
| 5 | a long period in | 9 |
|
| 6 | a long period during | 8 |
|
