— Why didn't you stay at __________ one?
A:a cheap
B:a cheaper
C:the cheap
D:the cheaper
如图所示,小灯泡规格为“5V 2.5W”(灯丝电阻的变化不计),闭合开关,当滑动变阻器的滑片移至a端时,电流表的示数为0.5A;当滑片移至b端时,电压表的示数为3V,则( )