Almost a seventh of China has been under heavy smog.

中国近七分之一的地区一直处于重度雾霾之下。

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The sky over the city was overspread with heavy smog.

城市上空罩上了一层浓重的烟雾。

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The sky over the city was overspread with a heavy smog.

城市上空罩上了一层烟雾。

《新英汉大辞典》

Finally, a heavy rain washed away the smog.

最后，一场大雨将烟雾荡涤干净。

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Finally, a heavy rain washed away the smog.

最后，一场大雨将烟雾荡涤干净。

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