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The level of pollution in the river was falling.
该河流受污染的程度其时正在降低。
《柯林斯英汉双解大词典》
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Another difficult question involves what level of pollution is safe.
另一个难题是什么样的污染水平是安全的？
youdao
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Another difficult question involves what level of pollution is safe.
另一个难题是什么样的污染水平是安全的？
youdao