单项选择题
A.1B.2C.3D.4
A.1/3B.1/2C.2/3D.3/4
A.电压高时电阻低,电压低时电阻高B.电压高时电阻高,电压低时电阻低C.电压高时电阻高,电压低时电阻高D.电压高时电阻低,电压低时电阻低