【单选题】
图所示电路中,已知φ<sub>a</sub>=9V,φ<sub>b</sub>=0,φ<sub>V</sub>,则U<sub>ab</sub>,U<sub>bc</sub>,U<sub>ac</sub>的值分别为()<br /> <img src="https://nimg.ppkao.com/2019-05/tangling/2019051414302946651.jpg?sign=807967adb5372f3fc09d719fc48885ad&t=62d5da2c" />
A、9V, 5V, 4V
B、9V, -5V, -4V
C、9V, -5V, 4V
D、9V, 5V, -4V