读图,回答问题。
下列实例中,为了减小有害摩擦的是( )
如图12—4所示,电源电压恒定, 当S接a时,电流表A1与A2的示数之比为3:5;当S接b时,电流表A1与A2的示数之比为2:3,则R2与R3的电阻之比为( )图12—4
This morning Ella called the manager to say that she was unable to work________a bad cold.