A:x<1
B:x>1
C:x≤1
D:x≥1
两只相同的白炽灯L1、L2接到如图所示的电路中,灯L1与电容器串联,灯L2与电感器串联,当a、b处接电压最大值为Um、频率为f的正弦交流电源时,两灯都发光,且亮度相同.更换一个新的正弦交流电源后灯L1的亮度大于灯L2的亮度,新电源的电压最大值和频率可能是( )
—Many students don't know how to____ stress and become worried.
—I think they should ask their parents for help.
图1为我国古代朝代更替示意图的片断摘录。图1中①②③代表的朝代分别别是( )