study slacker;weak student;slow student;
Waelz slag, to give its technical name, is composed mainly of silica but is also undesirably rich in poisonous metals like lead and zinc.
其学名称为waelz渣,主要由二氧化硅组成,但因同时含有丰富的诸如铅、锌等有毒金属而不受人欢迎。
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