硫化橡胶制劳保手套(发射科医生用)()
参考答案：4015.1900
When you are swimming, ________ your ears. You can use earplugs (耳塞) to stop water getting into your ears.
A．take after
B．take part in
C．take off
D．take care of
铝土矿的主要成分是氧化铝（化学式为Al2O3），
⑴在氧化铝中氧元素与铝元素的质量比为
⑵170吨含氧化铝80％的铝土矿中含铝元素的计算式为（杂质不含铝元素）
