如图所示的电路,断开开关S1、S2,闭合开关S3,灯L1(6V 3W)与灯L2(6V 6W)是____ 联;灯L1与灯L2两端的电压之比为____ ;断开开关S3,闭合开关S1、S2,灯L1与L2是____ 联.
明清政治制度的变革主要围绕( )
There are lots of ______ of art in the museum.