| 排序 | 环境成分 | 频次 |
| 1 | where | 13 |
| 2 | in 2021 | 10 |
| 3 | last year | 5 |
| 4 | when | 4 |
| 5 | directly | 4 |
| 6 | annually | 3 |
| 7 | historically | 3 |
| 8 | with a written demand | 3 |
| 9 | in September 2021 | 3 |