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阅读上面的材料，选择正确答案。 City Library's BOOK SALE October 11st - October 15th Oct. 11st 16:30-19:30 member (会员) only Oct. 12nd 10:00-19:30 Oct. 13rd 10:00-15:30 Oct. 14th 10:00-15:30 Oct. 15th 10:00-16:00 (＄9 Bag Day) The book sale on Oct. 11st is only for members of the City Library. Not a member? Sign up (报名) at Seymour's Bookstore in the library, or at the door of this sale! On the last day of the sale, you can buy a bag at＄9 here and take a bag of books home for free. Call 827-6950 with any questions. Welcome to the book sale! 如图所示电路中，开关S1、S2和S3原来都是断开的．要使灯L1、L2组成并联电路，应闭合的开关是______；若要使灯L1、L2组成串联电路，应闭合的开关是______；当同时闭合开关S1、S2、S3时，电路会发生______现象．