题目

电流在单位时间内做的功叫做电功率．是用来表示消耗电能的快慢的物理量，用户表示，它的单位是瓦特(Watt)，简称瓦，符号是W．纯电阻电路电功率P=UI＝12R＝U2/R，无论是串联电路还是并联电流，电路的总功率均等于各支路功率之和．如右图所示，在一个粗细均匀的金属圆环上有A、B、C、D 4个点，已知弧AD长为弧ACD长的一半，A、C两点等分圆珠的周长，如果分别(1)将A、C两点接人电路中，(2)将A、D两点接人电路中，并使两种情况中圆环上消耗的电功率相Sometimes it is impossible to deliver（投递）all the mail that arrives at the post office. Perhaps there is an mailing address and there is no return address. The post office cannot just the mail, so it becomes “dead mail”. Dead mail is to one of the U.S. Post Service’s in Atlanta, New York, and San Francisco. Seventy-five million pieces of mail can be put in these offices in one year.There the workers of the dead mail offices have ways to deal with all of these pieces of dead mail. First of all, they look for that can help them deliver the mail； they open packages, expecting that something will show where the package came from or is going to. Dead mail will also be listed on a so that people can call in and check to see if a missing thing is there on the screen. However, all of this mail cannot simply be forever； there is just too much of it. When a lot of dead mail comes together, the dead mail offices hold public auctions (拍卖). Every three months, some people who are are invited to the offices with objects found in dead mail packages and they are sold to the bidder (出价者).【1】A. impatient B. important C. unclear D. inactive【2】A. turn off B. eat up C. sell out D. throw away【3】A. sent B. returned C. lent D. sold【4】A. no B. various C. silly D. cruel【5】A. people B. time C. clues D. books