问题 单项选择题

在教师表中,如果要找出职称为“教授”的教师,所采用的关系运算是( )。

A.选择

B.投影

C.连接

D.自然连接

答案

参考答案:A

解析: 本题考查关系运算的知识。关系运算共可分为两大类,一类是传统的集合运算,如并、交、差和笛卡儿积:还有一类是专门的关系运算,其中包括选择、投影和连接。

阅读理解

阅读理解。

Hello Sandy,

     We have just returned from our holiday. We went with our friends Edward Smith and his wife Tina to

the Yorkshire Moors. This is a beautiful place. It is a natural park. There are lots of places to walk on the

tops of the hills, miles of grassland with no people, just sheep and birds.

     Edward, who had just come out of hospital, could not walk as far as he used to. However this meant

that we walked in the mornings, and then stopped at a cafe for lunch each day, before returning to the place

we live. Edward and I slept in front of the fire all afternoon, while the ladies went for another walk. Very

pleasant!

     I have taken lots of photos from the place we live, across the valley (峡谷) below us, of the morning

sunrise, and the mist in the valley. Also, in England, the old steam powered trains (蒸汽火车) are very

popular. I have taken many photos of the train and I really want to share them with you.

     Yesterday we had the first snow of this winter. It is very early (we usually expect snow in January). It

rained all day, and then snowed in the evening. Today we have bright sunshine!

     Both Jenny and I are well. I don't know if I told you, in the last E-mail, that Jenny is now working in a

hotel. Although she has to work hard, people there are nice and she is enjoying the work.

     Please write to us to tell us your news.

                                                                                                                                         Yours,

                                                                                                                                          Victor

1. What kind of place is the Yorkshire Moors? [ ]

A. A hotel.

B. A natural park.

C. A hospital.

D. A cafe.

2. When did the ladies take a walk? [ ]

A. Only in the morning.

B. Only in the afternoon.

C. Both in the morning and in the afternoon.

D. In the evening.

3. They had ______ snow this winter. [ ]

A. an early

B. a late

C. a usual

D. a big

4. What does the underlined word "them" in Paragraph 3 mean? [ ]

A. The valley.

B. Photos.

C. The mist.

D. The train.

5. What do we know from this passage? [ ]

A. This is the first time Victor wrote an e-mall to Sandy.

B. Edward didn't go traveling because he had just come out of hospital.

C. Jenny's new job in a hotel is an easy one.

D. People in England like the old steam powered trains very much.

单项选择题