25. 如圖(十七)所示電路,若R1 = 2 k Ω,R2 = 20 k Ω,R3 = 3 k Ω,R4 = 30 k Ω,Va = – 0.3V, Vb=0.2V,則輸出電壓Vo為何? (A) 5V (B) – 5V (C) 10V (D) – 10V