50. 右圖為理想放大器所構建之韋恩電橋(Wien-bridge)振 盪器,若R1 = 4 kΩ,R2 =1 kΩ,R4 = 10 kΩ,C1 = 0.1 μF ,C2 = 0.4 μF,該電路之回授量β應為多少? (A) (B) (C)(D)