A:二氧化碳
B:尿素
C:粪便
D:多余的无机盐
When he was unknown ________the young people, he served ________ a singer at a bar.
如果闭合电路中电源的电动势为12V,外电压为10V,当有0.5C电荷量通过电路时,下列结论正确的是( )