问题 单项选择题

关系数据库中,实现表与表之间的联系是通过______。

A.实体完整性规则

B.参照完整性规则

C.用户定义的完整性

D.值域

答案

参考答案:B

解析:完整性约束是关系数据库中不可缺少的组成部分,在关系数据库中存在三种类型的完整性约束。1、实体完整性约束:指关系(表)中的元组必须是惟一的,其码不能为空且不能重复;2、参照完整性约束:指关系(表)中引用的字段在另一个关系(表)中必须是已存在的或改字段为空, 它反映了两个表之间的联系;3、用户定义的完整性约束:指用户定义在关系上的特殊的约束,如性别字段只能是“男”或“女”; 值域指的是值的取值范围。故本题答案为B。

阅读理解

阅读理解。

     What is the relationship between violence and sports? Psychologists say that there are many

reasons for violence at sports events.One is alcohol.Many fans drink a lot at games.When

people drink, they are more likely to do abnormal things.Psychologist Dennis Brock says,

"Quiet people become loud.Normally nonviolent people become destructive. "

     David Sampson, a sports sociologist, says, "These are often celebratory riots- a large number

of very happy people mixed in with large amounts of alcohol.They don't often seem dangerous

in the beginning, but things get violent quickly. "

     Another reason for violence at sports events is the crowd.When individuals are in a large

group of people, they can lose their sense of personal responsibility.Edward Hirt, a social

Psychologist, says that research shows that people do things in crowds that they would never

do alone.People in crowds feel anonymous - no one knows who they are.Crowds also

make people feel powerful.They stop making personal decisions.They just follow the crowd.

Social psychologists call this a "mob mentality".

Dave Zarifis, head of public safety says, "Some people don't even come to celebrate.They want

to drink hard and make trouble.Someone does something stupid, and it grows from there.You

get a mob mentality.People think it's OK to do almost anything.They think, 'There are so many

of us and not enough of them. '

Social psychologist Dr.Sharon Kennedy says that there are some things officials can do to prevent

violence.Making sure that an area is not overcrowded is very important.Officials should also think

of games as "big parties." Then they will prepare differently.Kennedy says that in Great Britain they

are controlling the problem with cameras in all the stadiums."When you know someone is watching,

you are much less likely to behave badly. "

1. Which of the following best gives the main idea of the first two paragraphs?  

A. There's a connection between violence and sports

B. One cause of violence at sports events is alcohol.

C. There are many reasons for violence at sports events.

D. David Sampson and Dennis Brock have the same opinion.

2. Which of the following does NOT belong to a "mob mentality"?

A. "I must drink some alcohol to stop myself feeling shy. "

B. " It's safe to do what many people are doing. "

C. "There are so many of us and not enough of them. "

D. " No one knows I'm doing this. "

3. The last paragraph is mainly about ______.

A. how to turn games into big parties

B. why to install cameras in stadiums

C. how to prevent violence at sports events

D. how to avoid oneself behaving badly

4. What lesson can we learn from this passage?

A. Never drink any alcohol no matter where you are.

B. Whenever you are watching a game, you should keep quiet.

C. Never follow blindly no matter how many people are doing something.

D. Be careful when you are at a stadium because there are cameras there.

单项选择题