6.對一封閉電路的電壓降代數和為零是說明 (A)赫希克夫電壓律(Kirchhoff’s voltage law) (B) 庫倫電壓律(Coulomb’s voltage law) (C)法拉第電壓律(Farady’s voltage law) (D)歐姆定律(Ohm’s law)