问题 单项选择题

数据的独立性包括( )。

A.数据的结构独立性和组织独立性

B.数据的结构独立性和数据的逻辑独立性

C.数据的物理独立性和数据的逻辑独立性

D.数据的结构独立性和数据的物理独立性

答案

参考答案:C

解析: 数据的独立性是数据库领域的一个常用的术语,包括数据的物理独立性和数据的逻辑独立性。①数据的物理独立性是指用户的应用程序与存储在磁盘上的数据库中的数据是相互独立的,也就是说,当数据的物理存储改变时,应用程序不变。②数据的逻辑独立性是指用户的应用程序与数据库的逻辑结构是相互独立的,也就是说,数据的逻辑结构改变了,用户程序也可以不变。

论述题
阅读理解

阅读理解

                                                    

    The zebra belongs to the horse family.One of nature's great mysteries is why the zebra has stripes.One

theory is that the stripes help the zebra cool down.On hot days the black stripes get a lot hotter than the

white area of the zebra and under the black stripes there are special layers of fat for protection.Hot air then rises off the black stripes,forcing colder air down around the white areas,cooling the zebra down.This,

however,is just a theory.The stripes can also confuse predators (食肉动物) when zebras stay with other

animals in great numbers.

     Zebras have excellent hearing and eyesight and can run at a speed of up to 35 miles per hour (56

kilometers per hour).They also have a powerful kick that can cause serious injury to a predator,like a

lion,or an African wild dog.Usually the lead male of the herd stays at the back of the group to defend

against predators if necessary,while the females and youngsters run from danger.

     Zebras are herbivores and feed mostly on grasses,although they also might eat the leaves and stems (茎) of bushes a bit.They eat grasses for many hours each day,using their strong teeth.Spending so much

time chewing wears the zebra's teeth down,so their teeth keep growing all their lives.As the dry season

arrives and the grasses die back,zebra herds travel to find more food and water holes for drinking.Most

zebras have no specific territories.They travel from place to place,never staying in one area very long.

1. What can be inferred from the first paragraph?

A. There are different opinions about why the zebra has stripes.

B. The black stripes help the zebra live through cold days.

C. The zebra can easily be attacked by predators.

D. The zebra always travels with other animals.

2. According to the passage,herbivores are________.

A. animals that have specific territories

B. animals that only eat plants

C. animals that kill and eat other animals

D. animals that live in groups

3. The zebra has strong teeth all their lives because their teeth________.

A. only chew soft grasses

B. are used all day

C. are always growing

D. are kept clean

4. Which of the following statements about zebras is TRUE?

A. They have poor eyesight and hearing.

B. Their stripes can confuse predators.

C. They can run 56 miles per hour.

D. They usually stay in one area all their lives.

5. Which of the following TV programs might the passage be adapted for?

A. Hobbies & Leisure    

B. Everyday Tips

C. Digital Stadium      

D. Discoveries