问题 单项选择题

在关系模型中,为了实现“关系中不允许出现相同元组”的约束应使用

A.临时关键字

B.主关键字

C.外部关键字

D.索引关键字

答案

参考答案:B

解析: 本题考查主关键字的作用。在Visual FoxPro中,利用主关键字和候选关键字来保证表中的记录惟一,即保证实体惟一性,其他选项的几个关键字是错误的,外部关键字是用来保证参照完整性,而索引关键字并不能保证“关系中不允许出现相同元组”这一条件。因此选项B为正确答案。

阅读理解

When I was about 12, I had an enemy, a girl who liked to point out my shortcomings(缺点). Sometimes she said I was thin. Sometimes she said I was lazy. Sometimes she said I wasn’t a good student. Sometimes she said I talked too much, and so on. I tried to put up with(忍受) her as long as I could. At last, I became very angry. I ran to my father with tears in my eyes.

He listened to me quietly, and then he asked, “Are the things she said true or not? Mary, didn’t you ever wonder what you’re really like? Go and make a list of everything she said and mark the points that are true. Pay no attention to the other things she said.”

I did as he told me and to my surprise, I discovered that about half the things were true.

I brought the list back to my dad. He refused to take it. “That’s just for you,” he said. “You know better than anyone else the truth about yourself. When something said about you is true, you’ll find it will be helpful to you. Don’t shut your ears. Listen to them all, but hear the truth and do what you think is right.”

Many years have passed. The situation often appears in my mind. In our life we often meet with some trouble and we often go to someone and ask for advice. For some advice you will treasure(珍惜) all your life!

小题1:What did the writer’s father do after he heard her complaints(抱怨)?

A.He agreed with her “enemy”.

B.he let her continue to put up with her “enemy”.

C.He told her to write down all her “enemy” had said about her.

D.He told her not to pay attention to what her “enemy” had said.小题2:The writer felt ______ when she did the things as her father had told her.

A.surprised

B.angry

C.disappointed

D.sad小题3:Which of the following can we know from the passage?

A.The “enemy” thought the writer was pretty.

B.The “enemy” thought the writer studied hard.

C.The writer and her “enemy” became best friends at last.

D.The writer is grateful to her father.小题4:Which of the following can be the best title of the passage?

A.My Parents

B.A Serious Criticism(批评)

C.What People Say About You Is Always Right

D.The Best Advice I Ever Had

多项选择题