问题 单项选择题

并发操作有可能引起( )。 Ⅰ、丢失更新 Ⅱ、不可重复读 Ⅲ、读脏数据

A.仅Ⅰ和Ⅱ

B.仅Ⅰ和Ⅲ

C.仅Ⅱ和Ⅲ

D.都是

答案

参考答案:D

解析: 在数据库中使用并发执行的动机本质上与操作系统中使用多道程序的动机是一样的。当多个事务并发执行时,即使每个事务都单独地正确执行,数据库的一致性也可能被破坏。事务的并发执行可能出现的3个主要问题是:丢失更新、对未提交更新的依赖和不一致的分析,即包括丢失更新、不可重复读和读脏数据。

阅读理解

In Britain you may often hear “Drop in any time” or “Come to see me soon”, but you can’t really do that. People just say those things to make you feel welcome. It is better to telephone before visiting someone at home. If you receive a written invitation to an event that says “RSVP”, you should reply to let the person who sent the invitation know whether or not you plan to go.

You should never accept an invitation unless you really plan to go. You may refuse by saying, “Thank you for inviting me, but I will not be able to come.” If, after accepting, you are unable to go, be sure to tell those who are expecting you as soon as possible that you will not be there. Although it is not necessarily expected that you give a gift to your host, it is considered polite to do so, especially if you have been invited for a meal. Flowers, chocolate, or a small gift are all appropriate(合适的). A thank-you note or telephone call after the visit is also considered polite and is an appropriate way to express your appreciation for the invitation.

小题1:What can you do when a British friend says, “Drop in anytime”?

A.Visit him or her at any time.

B.Say no time to him or her seriously.

C.Telephone him or her before visiting.

D.Visit him or her soon.小题2:What does the underlined word “RSVP” probably mean in Chinese?

A.请自便

B.请回复

C.请审阅

D.请来访小题3:What should you do if your British friend sends you an invitation but you do not want to go?

A.Do not give him or her an answer.

B.Tell another friend to go instead of you.

C.Tell him or her that you can’t be there for some reason.

D.Tell him or her that you don’t want to go there.小题4:Which of the following is considered impolite in Britain?

A.Buy small presents when invited.

B.Refuse the invitation without telling anyone.

C.Write a thank-you note after a visit.

D.Give a telephone call after a visit.小题5:Where would you probably see this passage?

A.In an invitation.

B.In a guidebook.

C.On a poster.

D.In a newspaper.

单项选择题