二氧化硫是一种污染物，并且是形成酸雨的主要因素。
Sulphur dioxide is a pollutant and a major contributor to acid rain.
这种情况似乎是由许多因素的累积的结果，而大气污染物是主要的罪魁祸首。
The condition appears to result from the cumulative effect of a number of factors, with atmospheric pollutants the principal culprits.
应对主要的风险因素(包括营养不良和室内空气污染)与接种疫苗和母乳喂养一样，对预防肺炎是至关重要的。
Addressing the major risk factors - including malnutrition and indoor air pollution - is essential to preventing pneumonia, as are vaccination and breastfeeding.
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