2. 有三個電阻,大小分別為R1 、R2 、R3 ,今將其串聯在一起,則總電阻為多少?(A)R1+R2+R3 (B)R1×R2×R3 (C)(R1×R2×R3)/(R1+R2+R3)(D)(R1+R2+R3)/(R1×R2×R3)