PM2.5 had become less concentrated in recent decades thanks to air quality improvement measures.
由于采取了改善空气质量的措施，PM2.5的浓度在近几十年有所下降。
| 单词 | improvement measures |
| 例句 |
原声例句
当月 CNN 听力 PM2.5 had become less concentrated in recent decades thanks to air quality improvement measures. 由于采取了改善空气质量的措施，PM2.5的浓度在近几十年有所下降。 |
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