问题 填空题

设在关系模式R(A,B,C,D,E,F,G)中,根据语义有如下函数依赖集F=(A→B,C→D,C→F,(A,D)→E,(E,F)→G)。关系模式R的码是______。

答案

参考答案:(A,C)

解析: 候选码的定义是:设K为关系模式R<U,F>中的属性或属性组。若K→U在F+中,而找不到K的任何一个真子集K’,能使K’→U在F+中,则称K为关系模式R的候选码。本题易知C必然是主属性,再利用增广律逐个尝试可以知道(A,C)是候选码。

选择题

    北京时间2008年9月25日晚9时10分,中国自行研制的第三艘载人飞船神舟七号,在酒泉卫星发射中心发射升空。2008年9月27日16时43分,中国“神七”载人飞船航天员翟志刚顺利出舱,实施中国首次空间出舱活动,迈出了中国人太空行走的第一步。2008年9月28日17时37分,在距地球表面约343千米的近圆轨道上绕地飞行45圈后“神舟七号”载人飞船顺利返回地面,中国第三次载人航天飞行任务取得了圆满成功。据此回答1-7题。

1、升空后的“神舟七号”不属于下列哪个天体系统[ ]

A、总星系

B、河外星系

C、银河系

D、太阳系

2、远在美国纽约的晓华看到航天员翟志刚顺利出舱感到非常高兴。航天员顺利出舱时纽约(西五区)当

    地的区时是[ ]

A、28日5时43分

B、27日3时43分

C、27日19时43分

D、27日13时43分

3、在飞船飞行的这几天,太阳直射点的纬度位置和移动方向是[ ]

A、在北半球,向北移动

B、在北半球,向南移动

C、在南半球,向北移动

D、在南半球,向南移动

4、在飞船返回地面的这一天,温州的昼夜长短情况及其变化趋势是[ ]

A、昼长夜短,白昼在变长

B、昼长夜短,白昼在变短

C、昼短夜长,白昼在变短

D、昼短夜长,白昼在变长

5、在飞船返回地面的过程中,依次穿越哪几层大气层[ ]

A、平流层、对流层

B、对流层、平流层

C、高层大气、平流层、对流层

D、 对流层、平流层、高层大气

6、“神舟七号”飞船在飞行过程中可能受到来自太阳的太阳风、耀斑等太阳活动的影响,太阳风、耀斑

    分别出现于太阳大气的哪一层[ ]

A、日冕层、 * * 层

B、日冕层、光球层

C、 * * 层、光球层

D、光球层、 * * 层

7、太阳活动具有一定的周期性,其活动的周期大约是[ ]

A、9年

B、10年

C、11年

D、12年

阅读理解

As we all know, any country has good reasons to want its citizens to be as healthy as possible. This led to the introduction of a health service in many countries. France has developed into a country in which all citizens can get most of the health treatment free. The money for this is partly from the people who are willing to offer.

But there are different opinions about the Health Service. The number of patients treated every year and the cost of treatment are much greater than expected. This means that the people who work for the Health Service --- doctors, nurses and other hospital workers, have much more work to do, and as a result they have little time for preventive treatment.

However, the tough problem is that as many people are able to receive treatment more expensive than they can pay, sometimes people go and visit their doctors when they don’t really need to. As there are many patients, doctors cannot spend time long enough with each patient. So some people prefer to pay for their own treatment so that their doctors can examine them more carefully. In fact, some rich people feel that they should pay more free money, which would be given to other citizens.

小题1: France is described as an example to show that __________.

A.people have to pay part of the medical care

B.everyone in France enjoys free medical care

C.it is a country with the Health Service

D.it is a very rich country in Europe小题2: What is the problem in the Health Service?

A.Money is not enough to employ more medical workers.

B.There are not enough well-treated doctors.

C.People can get more preventive treatment.

D.Doctors and nurses are not working hard.小题3: Why do many people go and see the doctors even when they really don’t need to?

A.To keep himself even more healthy.

B.To receive treatment free of charge.

C.To take back some expensive medicine.

D.To get necessary protective treatment.小题4:What can we infer from the last paragraph?

A.The Health Service is quite successful so far.

B.People should not go to the doctors unless necessary.

C.There is much to improve the Health Service.

D.The rich should be allowed to pay for the treatment.