问题 单项选择题

以下关于主关键字的说法,错误的是 ______。

A.使用自动编号是创建主关键字最简单的方法

B.作为主关健字的字段中允许出现Null值

C.作为主关键宇的字段中不允许出现重复值

D.不能确定任何单字段的值得惟一性时,可以将两个或更多的字段组合成为主关键字

答案

参考答案:B

解析:[知识点] 数据库和表的摹本操作/表的建立
[评析] 为了使保存在不同表中的数据产生联系,Access数据库中的每个表必须有一个字段能惟一标识每条记录,这个字段就是主关键字。主关键字可以是一个字段,也可以是一组字段。为确保主关键字段值的惟一性,Access不允许在主关键字字段中存入重复值和空值。自动编号字段是在每次向表中添加新记录时,Access会自动插入惟一顺序号。库中若未设置其它主关键字时,在保存表时会提示创建主键,单击“是”按钮,Access为新建的表创建一个“自动编号”字段作为主关键字。

阅读理解

阅读理解。

     A young boy was playing with a ball in the street. He threw (扔) it too hard and it broke (打破) the

window of a house and fell (掉) inside. A woman came to the window and shouted (大喊) at the boy.

The boy was afraid and ran away. But he still wanted his ball back. A few minutes (分钟) later. The boy

came back and knocked (敲) at the door and said, "My father is going to come and repair (修理) your

window soon." 

     After a while, a man came to the door with tools (工具) in his hand, so the woman let the boy take his

ball away. 

     When the man finish repairing the window, he said to the woman, "Please pay ten dollars." 

     "But aren't you the father of the boy?" the woman asked, looking surprised (惊奇). "No," he

answered, looking more surprised, "Aren't you his mother?"

1. The boy lost his ball because _____. 

A. the ball fell into the woman's garden 

B. the ball broke the window of his house 

C. the ball broke the window and fell into the woman's house 

D. he went through the window of the woman's house

2. The boy ran away because _____. 

A. he was afraid of the woman  

B. he had to ask his father for help 

C. he didn't want his ball back        

D. he had to look for his friends

3. The boy came back again because _____.

A. he father will come soon                    

B. he wanted the ball back 

C. the woman was his mother          

D. a man would come to repair the window

4. The woman let the boy take his ball away _____. 

A. because she thought he was honest (诚实的) 

B. because he came back and repaired the window 

C. because she thought the man was his father 

D. because his father repaired the window

5. Which of the following is RIGHT? 

A. The boy was the son of the man. 

B. The man was the father of the boy. 

C. The woman knew the man was the father of the boy. 

D. The man thought the woman was the boy's mother.

探究题