A:English-spoken; English speaking
B:English-speaking; English spoke
C:speaking-English; English spoke
D:spoken-English; English speaking
根据以上信息,该班级选择“B”选项的有____.
如图所示,三只完全相同的灯泡a、b、c分别与电阻R、电感L、电容C串联,再将三者并联,接在220V,50Hz的交变电源两端,三只灯泡亮度相同.如果将电源改为220V,60Hz的交变电源,则( )