题目

Sometimes just when we need the power of miracles, they arise in the places we would least expect.On a cold January afternoon in 1989, I was climbing Egypt’s Mt. Horeb, hoping to get to the peak by sunset to see the valley below. As I was winding up the narrow path, I’d sometimes see other hikers who were coming down. While they would generally pass with simply a nod or a greeting in another language, there was one man who did neither.I saw him coming and as he got closer, I could see that, unlike other hikers, he was wearing traditional Egyptian galabia( 长 袍 ). What made his appearanc如图所示，闭合开关S2，灯L1和L2是 ；闭合开关S1和S3，灯L1和L2是 ．（选填“串联”或“并联”）