C:电池工作时,电子由正极通过外电路流向负极
A:电池工作时,锌失去电子
B:电池正极的电极反应式为:2MnO2+2H2O+2e-==2MnOOH+2OH-
D:外电路中每通过0.2 mol电子,锌的质量理论上减少6.5 g
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The Americans took about five days to get to there. ____
如果 3a+12是二次根式,那么a的取值范围是( )