50. 圖(三十)所示之電晶體直流偏壓電路,若 =0.7V,β=150, =15V, =300kΩ, =1kΩ, =0.51kΩ,則其直流工作點與之值各約為何? (A) =1.2mA、 =13.2V (B) =3.8mA、 =9.3V (C) =5.7mA、 =6.4V (D) =7.8mA、 =3.2V