如图所示电路中.
(1)要使灯L1﹑L2串联,则只闭合开关______;
(2)闭合S1﹑S2断开S3,则灯L1﹑L2是______联;
(3)能单独点亮的灯是______,这时应闭合开关______;
(4)如果同时闭合开关S1﹑S3,则会发生______.