问题 单项选择题

在指定字段或表达式中不允许出现重复值的索引是______。

A.惟一索引

B.惟一索引和候选索引

C.惟一索引和主索引

D.主索引和候选索引

答案

参考答案:D

解析:主索引和候选具有关键字特性,其字段值可以保证惟一性。它拒绝重复字段。惟一索引和普通索引允许字段出现重复值。但惟一索引中重复的索引字段值只有惟一一个值出现在索引项中。所以在指定字段 或表达式中不允许出现重复值的索引是主索引和候选索引。

选择题
阅读理解

第三部分阅读理解(共15小题,每小题2分,共30分)

阅读下列短文,从每题所给的A、B、C、D四个选项中,选出最佳选项。

Once there was an old man in a town.He always forgot a lot of things.So his wife always had to say to him, “Don’t forget this!”

One day he went on a long trip alone.Before he left home,his wife said, “Now you have all these things.They are what you need for your trip.Take care of your things during the trip.”He went to the station,bought a ticket and got on the train with it.

About half an hour later,the conductor began to check the tickets.He came to the old man and said, “Will you please show me your ticket?”The old man looked for his ticket in all his pockets,but he could not find it.He was very worried. “I can’t find my ticket.Ireally bought a ticket before I got on the train.”said the old man.

“I believe you bought a ticket.All right,you don’t have to buy another one.”said the conductor kindly. “But how can I know where I’m going?----I can’t remember my station!”the old man said sadly.

51.The old man in the story was very__________.

A. kind          B.poor            C.forgetful           D.sad

52.Where is the ticket?           

A.The old man forgot to buy it.

B.The old man could not remember where it was.

C.The old man showed it to the conductor.

D.The old man’s wife took the ticket away.

53.The old man bought the ticke__________he got on the train.

A.before           B.after            C.as           D. when

54.The conductor__________the old man.

A.didn’t believe           B.laughed at            C.believed           D.felt soory for

55.The old man was sad because_____________.

A.he sad to buy another ticket            B.he lost all the things his wife gave him

C.he did not know where he was          D.he did not know where he should get off