—I have a fever.
A:How are you doing?
B:Are you all right?
C:What's the matter with you?
D:Do you have a fever?
探究“一定电压下,电流与电阻的关系”.提供的实验器材有电源(电压恒为4.5V),电流表、电压表各一个,开关一个,三个定值电阻(10Ω,15Ω,20Ω),滑动变阻器一个(40Ω,1A),导线若干.