有四个命题：
①等弧所对的圆周角相等；
②圆周角相等，相对的弧也相等；
③平分弦的直径垂直于弦；
④三点确定一个圆，
其中错误的有（ ）
A．1个
B．2个
C．3个
D．4个
①在同圆或等圆中，等弧所对的圆周角相等，原说法缺少条件，故错误；
②在同圆或等圆中，圆周角相等，相对的弧也相等，原说法缺少条件，故错误；
③平分弦的直径垂直于弦，这个弦需要排除直径，原说法错误；
④不在同一直线上的三点确定一个圆，原说法缺少条件，故错误；
综上可得错误的有4个．
故选D．
完形填空 先通读下面的短文，掌握其大意, 然后从下面四个答案中选择可以填入 相应空白处的最佳答案。 (本大题共10分，每小题1分) 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).
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