| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | be [vb pp] [prep] a | 14911 |
|
| 2 | must be [vb pp] [prep] | 4919 |
|
| 3 | must be [prep] a | 104 |
|
| 4 | must be [vb pp] a | 53 |
|
