三相三线电能表有功功率表达式()：
A.P=UABIAcos(30°+φ)+UCBICcos(30°-φ)B.
B.P=UABIAsin(30°+φ)+UCBICsin(30°-φ)C.
C.P=UABIAtg(30°+φ)+UCBICtg(30°-φ)D.
D.P=UABIActg(30°+φ)+UCBICctg(30°-φ)
正确答案是A