单选题 图示电路中，已知i=[2+3sin(wt+30°)]A，R=4W，，则电压u为 A、9sin(wt-60°)V B、[8+9sin(wt-60°)]V C、[8+7.2sin(wt-23.1°)]V D、[8+15sin(wt-6.9°)]V