41. 如圖【5】所示之電路,若 = 15V,R1 = R3 = 10kΩ,R2 = R4 = 20kΩ,V1 = 8V,V2 = 5V, 則Vo為多少? (A) – 6V (B) – 3V (C) + 3V (D) + 6V