【单选题】
三相三线有功电能表,测量的有功功率表达式为()。
A、UabIacos(300+)+UcbIccos(300–)
B、UabIacos(300–)+UcbIccos(300+)
C、UabIacos(+300)+UcbIccos(–300)
A、UabIacos(300+)+UcbIccos(300–)
B、UabIacos(300–)+UcbIccos(300+)
C、UabIacos(+300)+UcbIccos(–300)