12. 如圖(七)所示之變壓器耦合串級放大器，假設Rs = 1 kΩ，RL = 200Ω，且基本放大器之電壓增益Av= 10 V/V，輸入阻抗Ri = 4 kΩ，輸出阻抗Ro = 1.8 kΩ，若要得到最大功率轉換，則變壓器線圈之圈數比N1: N2與N3:N4分別為何？ (A) N1: N2= 2: 1，N3:N4 = 3: 1 (B) N1: N2 = 1: 2，N3:N4 = 3: 1 (C)N1: N2= 1: 4，N3:N4 = 9: 1 (D)N1: N2 = 1: 4，N3:N4 = 1: 3