下图所示直流电路,电流I<sub>1</sub>,I<sub>2</sub>,I<sub>3</sub>满足的方程是()。<br /> <img src="https://nimg.ppkao.com/2017-07/zhangweibo/2017071517350860715.jpg?sign=3f34069ae736f69d75dffe7933775d9a&t=62d6de1f" />
A、I1-I2+I3=5A
B、I1-I2+I3=-5A
C、-I1+I2-I3=0
D、I1+I2+I3=0