In 2001,the annual average of NO2 concentration in the air of 341 cities attained the Grade II national standards for air quality.是什么意思_In 2001,the annual average of NO2 concentration in the air of 341 cities attained the Grade II national standards for air quality.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句