图中的灯泡在通电时,灯泡能被点亮。请在下面横线上填写当开关K1、K2处于以下状态时,灯泡A、B的亮熄情况:
(1)K1断开,K2闭合时_______________________________________________________;
(2)K1闭合,K2断开时_______________________________________________________;
(3)K1和K2都闭合时_______________________________________________________。