问题 单项选择题

下列对于关系的叙述中,不正确的是______。

A.关系中的每个属性是不可分解的

B.在关系中元组的顺序是无关紧要的

C.任意的一个二维表都是一个关系

D.每一个关系仅有一种记录类型

答案

参考答案:C

解析:一个关系对应一个二维表,但一个二维表不一定都能成为一个关系,如复式表格(数据项下还有子 项)就不是一个关系,只有符合一定要求的二维表才是关系。

完形填空

Thousands of years ago,human(人类)didn’t live in towns.Sometimes they would live in caves(洞穴)or build camps in the forest.

Only about thirty people  1   in each camp.The men would go hunting while the woman and children  2 food from trees around the camp.All the food was  3 among people in the group.Every few weeks they moved to another place to find more food.It was a simple life,but people had to be  4They had to make everything that they needed,and they had to know a lot about plants and animals.

Nowadays most people live in towns and cities,and they work in offices and factories.Life isthan in the old days.There are fewer  6 ,but there is less excitement.Some people go  7 excitement  sailing round the world.climbing mountains,or exploring(探测)caves.

Most people look forward to the  8 ,a time when they can enjoy a change from the normal life.For some this means going camping.But camping today is  9 from camping in the past.Gas cookers,ready-made food and air-beds mean people can camp much more  10 than they did in the old times.

1.A.lived         B.talked       C.came        D.danced

2.A.planted       B.collected     C.watched     D.bought

3.A.found        B.used         C.shared      D.sold

4.A.polite        B.kind         C.calm       D.clever

5.A.worse        B.faster        C.easier       D.harder

6.A.dangers       B.stories       C.people      D.animals

7.A.waiting for    B.looking for    C.turning on   D.putting on

8.A.dreams       B.gifts         C.meals       D.holidays

9.A.away        B.different       C.free        D.far

10.A.slowly       B.terribly        C.comfortably  D.hopefully

单项选择题