18 圖二為圖一所示電路之等效 T 型電路，則圖二中之三個等效電阻 RR2及 R3各為多少 Ω？ 
(A) R1 = 0.3 Ω，R2 = 0.6 Ω，R3 = 1.8 Ω
(B) R1 = 0.6 Ω，R2 = 0.3 Ω，R3 = 1.8 Ω
(C) R1 = 2 Ω，R2 = 10 Ω，R3 = 8 Ω
(D) R1 = 3 Ω，R2 = 18 Ω，R3 = 6 Ω