B:14V电路如图，网孔4的电流方程是（）。C:-14VA:2Im4+Im2+Im3=-0.5U1 B:2Im4-Im2-Im3=0.5U1 C:2Im4-Im2-Im3=-0.5U1 D:2Im4-Im2-Im3=0 答案: 2Im4-I