Don't speak. They ___________ to the radio.[ ]
A. listen
B. are listening
C. to listen
答案:B
当三相三线电路的中性点直接接地时,宜采用()的有功电能表测量有功电能。
A.三相三线;
B.三相四线;
C.三相三线或三相四线;
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