A:亚洲
B:欧洲
C:非洲
D:南美洲
She had no money ________ a birthday present for her children.
如图所示的电路中,电阻R1的阻值是5欧姆,干路中的电流I是0.5安培,电阻R2两端的电压是2伏特.求:
(1)通过R1的电流.
(2)通过R2的电流.
(3)R2的电阻值.