问题 单项选择题

关于下列关系的叙述中,不正确的是()。  职员关系是S(S#,SNAME,SEX.AGE)主码为S#  部门关系是C(C#,CNAME)主码为C#  职员部门关系是SC(S#,C#,r emark)主码为(S#,C#)

A.SC.C#是外码

B.SC.S#是外码

C.S是SC的参照关系

D.C是SC的目标关系

答案

参考答案:D

解析:关系中的某个属性不是该关系的主码或只是主码的一部分,但却是另一个关系的主码时,称该属性为外码。参照关系也称从关系,被参照关系也称主关系,他们是指以外码相关联的两个关系。注意:由于SC.C#是外码,而C的主码为C#,所以5和C都是SC的参照关系,故D)不正确。

阅读理解

In England, people often talk about the weather because they can experience (经历) four seasons in one day. In the morning the weather is warm just like in spring. An hour later black clouds come and then it rains hard. The weather gets a little cold. In the late afternoon the sky will be sunny, the sun will begin to shine, and it will be summer at this time of a day.

In England, people can also have summer in winter, or have winter in summer. So in winter they can swim sometimes, and in summer sometimes they should take warm clothes.

When you go to England, you will see that some English people usually take an umbrella (伞)or a raincoat with them in the sunny morning, but you should not laugh at them.

If you don't take an umbrella or a raincoat, you will regret (后悔) later in the day.

小题1:Why do people in England often talk about the weather?

A.Because they may have four seasons in one day

B.Because they often have very good weather

C.Because the weather is warm just like in spring

D.Because the sky is sunny all day小题2:From the story we know that when _________come, there is a heavy rain.

A.sunshine and snow

B.black clouds

C.summer and winter

D.spring and autumn小题3:"People can also have summer in winter." Means "it is sometimes too _____in winter."

A.warm

B.cool

C.cold

D.rainy小题4:In the sunny morning some English people usually take a raincoat or an umbrella with them because ________.

A.their friends ask them to do so

B.it often rains in England

C.they are going to sell them

D.they are their favourite things小题5:The best title (标题)for this passage is ________.

A.Bad Seasons

B.Summer or Winter

C.The Weather in England

D.Strange English People

单项选择题