| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | have been building up [prep] | 27 |
|
| 2 | [vb past] been building up [prep] | 14 |
|
| 3 | had been building up [prep] | 14 |
|
| 4 | [vb -s] been building up [prep] | 10 |
|
| 5 | 's been building up [prep] | 6 |
|
