| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | a period [prep] | 2664 |
|
| 2 | [v-ing] a period | 75 |
|
| 3 | [v-ing] a [prep] | 25 |
|
| 4 | [v-ing] period [prep] | 12 |
|
