— ?
—She is having coffee.
A:What does she do
B:What is she going to do
C:What does she like doing
D:What is she doing
如图所示,合上电键S1.当电键S2闭合时,电流表的示数为0.75A;当电键S2断开时,电流表的示数为0.5A,R1=R2=2Ω.求电源电动势E和内电阻r.
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