【单选题】
I regret()that I'm unable to help you.
A、saying
B、to say
C、say
D、said
A、saying
B、to say
C、say
D、said
A、A.Yes,I will. B、B.That’s great. C、C.I’m afraid I won’t be free. D、D.Is it all right?
A、正向故障时△U/△I=ZL+ZSN,反向故障时△U/△I=-ZSM B、正向故障时△U/△I=ZL+ZSN,反向故障时△U/△I=-ZSN C、正向故障时△U/△I=-ZSN,反向故障时△U/△I=ZL+ZSM D、正向故障时△U/△I=-ZSM,反向故障时△U/△I=ZL+ZSM