单项选择题
A.电压、电流B.电压、电阻C.电流、电阻D.电流、电场
A.连续可调、断续可调B.连续可调、步进可调C.断续可调、步进可调D.断续可调、前进可调
A.0.1%-0.5%B.0.2%-0.5%C.0.3%-0.5%D.0.4%-0.5%