13.已知N通道JFET工作於飽和夾止區，其閘源電壓VGS=-1.5V、截止電壓VGS(off)=-3V，IDSS=9mA，則輸出電流ID=？ (A)1mA (B)1.25mA (C)2.25mA (D)4.5mA

19.非反相放大器中，R1為反相輸入端至接地端的電阻，Rf為反相輸入端至輸出端的電阻，下列何者是其輸出電壓與輸入電壓的關係式？ (A)\( \frac{V_o}{V_i} = \# \frac{R_f}{R_1} \)(B)\( \frac{V_o}{V_i} = 1 + \frac{R_f}{R_1} \)(C)\( \frac{V_o}{V_i} = \# - 1 \)(D)\( \frac{V_o}{V_i} = \# \frac{R_1}{R_f} \)