问题
单项选择题
4只小鸟飞人4个不同的笼子里去，每只小鸟都有自己的一个笼子(不同的鸟，笼子也不同)，每个笼子只能飞进一只鸟。若都不飞进自己的笼子里去，有( )种不同的飞法。
A．16
B．15
C．12
D．9
答案
参考答案：D
解析： 第1只鸟除了自己的笼子不能进，有3种选择；第2只鸟也有3种选择；剩下的2只鸟只有1种选择。故不同的飞法共有3×3=9种。
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4只小鸟飞人4个不同的笼子里去，每只小鸟都有自己的一个笼子(不同的鸟，笼子也不同)，每个笼子只能飞进一只鸟。若都不飞进自己的笼子里去，有( )种不同的飞法。
A．16
B．15
C．12
D．9
参考答案：D
解析： 第1只鸟除了自己的笼子不能进，有3种选择；第2只鸟也有3种选择；剩下的2只鸟只有1种选择。故不同的飞法共有3×3=9种。
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| I can still remember when I met my best friend. She had just moved into the neighborhood and her grandmother brought her down to 1 me. I hid behind my mother and she hid behind her grandmother, 2 to look at each other. Soon we lost the 3 and started playing with each other. In the 7th grade, I first lost touch with her. She was 4 family problems and I deserted her to be with the 5 people. None of my new friends liked her as much as I did because they knew she had 6 . However, every summer we 7 always sit at each other's house and watch soap operas, and talk about all the boys we liked. It was last year when I noticed the problem. I guess l was 8 devoted in high school to 9 she needed someone there for her. Anyway, she made a new best friend and so did I. Then I didn't know why, 10 she started cutting herself! She then was diagnosed (诊断) with clinical depression At first, I was very 11 , but we still stayed in 12 . I wanted to be there for her since her new best friend basically 13 her and people were calling her 14 . Yesterday she came to me and said:"I never knew what a best friend was 15 you were the only person that would stop me cutting. I 16 you so much, and you didn't even know you were 17 me." We both cried. And I guess a kind of 18 from my life so far is never to give up on your friends. Even if they aren't as cool as others, or people think they are crazy, they need 19 there. If you desert them, you will only be 20 yourself. | ||||
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