A:②①
B:②④
C:③④
D:③①
在如图所示的电路中,电源电压和定值电阻R的阻值都保持不变,闭合开关,当滑片由A端滑到B端的过程中()
A.Mar.12th B.Apr.21st C.Oct.30th D.Feb.20th
E.May23rd F.Jun.20th G. Jul. 21st H. Dec. 23rd