三相四线电能表有功功率表达式( ):
A.P=UAIACosφA+UBIBCosφB+UCICCosφC
B.P=UAIAsinφA+UBIBsinφB+UCICsinφC
C.P=UAIAtgφA+UBIBtgφB+UCICtgφC
D.P=UAIACtgφA+UBIBCtgφB+UCICCtgφC
正确答案是A