| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | be [vb pp] [prep] [be] [v-ing] | 931 |
|
| 2 | must be [vb pp] [prep] [v-ing] | 141 |
|
| 3 | must be [vb pp] [prep] [be] | 70 |
|
