A:工业用SiO2与焦炭制取单质硅过程中,生成的气体产物是CO
B:硫在空气中燃烧的产物是SO2,在纯净氧气中燃烧的产物是SO3
C:钠在敞口容器中长期存放和在空气中燃烧的产物都是Na2O2
D:镁在空气中和纯净氧气中燃烧的产物都只有MgO
They should do exercises as ________ as possible to keep _________.