单项选择题
A.0.25mm~0.35mmB.0.5mm~0.65mmC.0.15mm~0.25mmD.0.35mm~0.5mm
A.分接开关B.变压器油C.绕组D.铁芯
A.B=FL/IB.B=F/ILC.B=FI/LD.B=IL/F