A:can’t
B:mustn’t
C:needn’t
D:shouldn’t
电流表G(满偏电流为300μA,内阻为100Ω);
电压表V1(量程为2V,内阻约为2000Ω);
电阻箱R1(阻值范围0~9999Ω);
电阻箱R2(阻值范围0~999.9Ω);
滑动变阻器R3(最大阻值为100Ω);
滑动变阻器R4(最大阻值为100kΩ);
电源E(电动势6V,内阻约0.5Ω);
单刀单掷开关S,导线若干.
—How did you get the unusual stamp?
—My pen friend in France sent it to me last year.