当S接a或接b时,电源电压恒定,对R1的电流无影响都为I1,
当S接a时 由A1与A2示数之比是3:5知,I1:I2=3:2,则R1:R2=2:3.
当S接b时,由A1与A2示数之比是2:3知,I1:I3=2:1,则R1:R3=1:2,故R2:R3=3:4
故选C.
当S接a或接b时,电源电压恒定,对R1的电流无影响都为I1,
当S接a时 由A1与A2示数之比是3:5知,I1:I2=3:2,则R1:R2=2:3.
当S接b时,由A1与A2示数之比是2:3知,I1:I3=2:1,则R1:R3=1:2,故R2:R3=3:4
故选C.