| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | a long period [prep] | 216 |
|
| 2 | a long period of | 183 |
|
| 3 | a long period of | 183 |
|
| 4 | a long period in | 7 |
|
| 5 | a long period in | 7 |
|
| 6 | a long period during | 6 |
|
| 7 | a long period during | 6 |
|
