A:couldn’t have stayed u
B:mustn’t have stayed u
C:shouldn’t have stayed u
D:needn’t have stayed u
如图1所示是电阻R1与滑动变阻器R的电路图,电源电压为12V,电阻R1的I﹣U图象如图2所示.开关闭合后,滑动变阻器R接入电路的阻值为40Ω时,求:
下列有机物的名称肯定错误的是( )