谐波源是指向( )注入谐波电流或在( )中产生谐波电压的电气设备。
A.动力电网,供配电网
B.公用电网,照明电网
C.公用电网,动力电网
D.公用电网,公用电网
参考答案:D
Is that man your teacher? [ ]
A. Yes, he is.
B. Yes, she is.
C. No, she isn't.