问题 单项选择题

下列有关数据库的描述,正确的是( )。

A.数据处理是将信息转化为数据的过程

B.数据的物理独立性是指当数据的逻辑结构改变时,数据的存储结构不变

C.关系中的每一列称为元组,一个元组就是一个字段

D.如果一个关系中的属性或属性组并非该关系的关键字,但它是另一个关系的关键字,则称其为本关系的外关键字

答案

参考答案:D

解析:数据处理是指将数据转换成信息的过程,故选项A)叙述错误;数据的物理独立性是指数据的物理结构的改变,不会影响数据库的逻辑结构,故选项B)叙述错误;关系中的行称为元组,对应存储文件中的记录,关系中的列称为属性,对应存储文件中的字段,故选项C)叙述错误。

阅读理解

阅读短文,选择正确答案。

      Now satellites are helping to forecast (预报) the weather. They are in space, and they can reach any part

of the world. The satellites take pictures of the atmosphere (大气), because this is where the weather forms

(形成). They send these pictures to the weather stations. So meteorologists (气象学家) can see the

weather of any part of the world. From the pictures, the scientists can often say how the weather will change.

      Today, nearly five hundred weather stations in sixty countries receive satellite pictures. When they receive

new pictures, the meteorologists compare (比较) them with earlier ones. Perhaps they may find that the clouds

have changed during the last few hours. This may mean that the weather on the ground may soon change, too.

In their next weather forecast, the meteorologists can say this.

      So the weather satellites are a great help to the meteorologists. Before satellites were invented, the scientists

could forecast the weather for about 24 or 48 hours. Now they can make good forecasts for three or five days.

Soon, perhaps, they may be able to forecast the weather for a week or more ahead (提前).

1. Satellites travel _______. [ ]

A. in space

B. in the atmosphere

C. above the ground

D. above space

2. Why do we use the weather satellites to take pictures of the atmosphere? Because _______. [ ]

A. the weather satellites can do it easily

B. clouds form there

C. the weather forms there

D. the pictures can forecast the weather

3. Meteorologists forecast the weather _______. [ ]

A. when they have received satellite pictures

B. after they have compared new satellite pictures with earlier ones

C. before they received satellite pictures

D. during they study satellite pictures

4. Maybe we'll soon be able to forecast the weather for _______. [ ]

A. one day

B. two days

C. five days

D. seven days or even longer

5. The main (主要的) idea of this passage is that satellites are now used in _______. [ ]

A. taking pictures of the atmosphere

B. receiving pictures of the atmosphere

C. doing other work in many ways

D. weather forecasting

填空题