给定关系模式R（U，F），其中，属性集U={城市，街道，邮政编码}，函数依赖集F={（城市，街道）→邮政编码，邮政编码→城市}。关系R（1），且分别有（2）。
空白（2）处应选择（）
A.1个非主属性和2个主属性
B.0个非主属性和3个主属性
C.2个非主属性和1个主属性
D.3个非主属性和0个主属性
参考答案：B
解析：分析本题考查关系数据库规范化理论方面的基础知识。空白（1）处的正确答案是C。因为根据函数依赖定义，可推出（城市，街道）→U，（邮政编码，街道）→U，所以“城市，街道”和“街道，邮政编码”为候选关键字。空白（2）处的正确答案是B。因为根据主属性的定义，“包含在任何一个候选码中的属性叫做主属性（Primeattribute），否则叫做非主属性（Nonprimeattribute）”，所以关系R中的3个属性都是主属性，而无非主属性。
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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, watch soap operas, and talk about all the boys we liked. It was last year when I noticed the problem. I guess I was 8 devoted in high school to 9 she needed someone there. 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 with 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, the only person, would stop me cutting. I 16 your help 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. | |||
| ( )1. A. follow ( )2. A. scared ( )3. A. temper ( )4. A. taking up ( )5. A. happier ( )6. A. problems ( )7. A. should ( )8. A. much ( )9. A. admit ( )10. A. but ( )11. A. calm ( )12. A. place ( )13. A. confused ( )14. A. crazy ( )15. A. unless ( )16. A. expect ( )17. A. urging ( )18. A. honour ( )19. A. someone ( )20. A. innocent | B. meet B. annoyed B. interest B. getting through B. cooler B. shortcomings B. could B. too B. accept B. for B. considerate B. touch B. bothered B. stubborn B. as B. influence B. blaming B. favour B. something B. successful | C. join C. worried C. confidence C. going through C. stronger C. partners C. would C. only C. consider C. or C. upset C. control C. reminded C. clumsy C. until C. appreciate C. helping C. pleasure C. anyone C. guilty | D. support D. delighted D. shyness D. making up D. cleverer D. disabilities D. might D. just D. realize D. so D. helpful D. mood D. deserted D. stupid D. that D. demand D. hurting D. lesson D. everything D. reliable |