问题 单项选择题

扫描仪是将图片、照片或文字等输入到计算机中的一种输入设备。下面是有关扫描仪的叙述:  Ⅰ.光学分辨率是扫描仪的一个重要性能指标  Ⅱ.所有扫描仪都能扫描照相底片等透明图件  Ⅲ.扫描仪的工作过程主要基于光电转换原理  Ⅳ.滚简式扫描仪价格便宜、体积小,适合于家庭使用  上面哪些叙述是正确的?

A.Ⅰ、Ⅱ和Ⅲ

B.Ⅰ和Ⅲ

C.Ⅱ和Ⅲ

D.Ⅱ和Ⅳ

答案

参考答案:B

解析:函数依赖是事物之间相关性的一种表述,是属性固有语义的体现。设R(U)是属性集U上的关系模式,X,Y,Z是U的子集。若对R(U)的任意一个可能的关系r,r中不可能存在两个元组在X上的属性值相等,而在Y上属性值不等,则称“X函数确定Y”或“Y函数依赖于X”,记作X→Y,X称为决定因素。

阅读理解

Accidents happen almost every day. Some accidents are not serious and some are. We read about such accidents nearly every day in the newspapers. It is wrong for people to think that accidents take place only on the roads or highways, or even at work places. Home accidents are just as common. Because very few home accidents are reported, people come to think that there are few accidents which happen in homes.

There have been many cases where people fall to their deaths from high rise flats. Children often fall over while coming down the stairs. Old people may slip (滑跤) on wet floors if they are not careful.

Nowadays there are a lot of modern electrical appliances (电器) such as rice cookers which make life easy for the modern house wives. These appliances can kill if they are not used in the proper way. Gas stoves (煤气灶) used for cooking are also dangerous if they are not properly used. They may cause burns or, in more serious cases, even fires.

But all such accidents can be stopped if we are careful and follow simple rules of safety. For example, it is unwise for people to try repairing their own electrical appliances if they do not know how to. It is safer to get them repaired by an electrician (电工).

小题1:Accidents take place ____.

A.mostly in homes

B.mostly on roads and highways

C.mostly in factories

D.almost everywhere小题2:Which of the following accidents may NOT happen in homes?

A.People may fall to death from high buildings.

B.People may be knocked down by cars on the roads.

C.Gas stoves may cause burns or even fires.

D.People may be killed by an electrical appliance.小题3:People are advised____ .

A.to avoid using electrical appliances

B.to repair their own electrical appliances

C.not to repair their own electrical appliances

D.not to get their electrical appliances fixed

单项选择题