单项选择题

在正弦交流电路中，电感元件上电压与电流的相位关系为（）。

A．电压超前电流90°
B．电压滞后电流90°
C．电压和电流同相位

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单项选择题

当μ的取值为（）时，子载波间隔为60kHz。

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How do debaters select their positions?

A．The positions are decided by the head judge.
B．The positions are selected by the debaters in turn.
C．The positions are given to debate teams at random.
D．The positions are arranged according to the ranking in previous debates.