题目如图所示电路,电源电压恒定不变.当S1S_{1}S1闭合、S2S_{2}S2断开时,电压表的示数为3V3V3V;当S1S_{1}S1断开、S2S_{2}S2闭合时,电压表的示数9V9V9V,则R1R_{1}R1:R2R_{2}R2为( )A.1:21:21:2B.2:12:12:1C.1:31:31:3D.3:13:13:1知识点:电路的简化与计算章节:能量 / 欧姆定律