问题 单项选择题

在多个用户共享数据库时,对同一资料的 (1) 操作可能破坏数据库的 (2) 。因此数据管理机制要解决丢失更新、不一致以及 (3) 等问题。解决的方法主要有加锁技术和时标技术。

1()

A.连接

B.并发

C.查询

D.更新

答案

参考答案:B

解析:

并发操作是指多用户共享的系统中,许多用户可能同时对同一数据进行操作。并发操作带来的问题是数据的不一致性。数据的不一致性主要有三类:丢失更新、不可重复读和读脏数据。其主要原因是事务的并发操作破坏了事务的隔离性。故选B、C、A。

阅读理解

阅读理解

     For years I wanted a flower garden. I'd spend hours thinking of different things I could plant that

would look nice together.

     But then we had Matthew. And Marvin. And the twins,    Alisa and Alan. And then Helen. Five

children. I was too busy raising them to grow a garden.

     Money was tight,  as well as time. Often when my children were little,    one of them would want

something that cost too much,    and I'd have to say,    "Do you see a money tree outside?Money

doesn't grow on trees,    you know."

     Finally,   all five got through high school and college and were off on their own. I started thinking

again about having a garden.

     I wasn't sure,  though. I mean,   gardens do cost money,    and after all these years I was used to

living on a pretty lean,   nofrills budget.

     Then,  one spring morning,    on Mother's Day,  I was working in my kitchen. Suddenly,  I realized

that cars were tooting their horns as they drove by. I looked out of the window and there was a new

tree,   planted right in my yard. I thought it must be a weeping willow,    because I saw things blowing

around on all its branches. Then I put my glasses on-and I couldn't believe what I saw. There was a

money tree in my yard!

     I went outside to look. It was true!There were dollar bills,    one hundred of them,    taped all over

that tree. Think of all the garden flowers I could buy with one hundred dollars! There was also a note

attached:"IOU eight hours of digging time. Love,    Marvin."

     Marvin kept his promise,  too. He dug up a nice tenbyfifteen foot bed for me. And my other children

bought me tools,    ornaments,  a trellis(棚架),  a sunflower stepping stone and gardening books.

     That was three years ago. My garden's now very pretty,  just like I wanted. When I go out and

weed or tend my flowers,    I don't seem to miss my children as much as I once did. It feels like they

are right there with me.

     I live up in Michigan's Upper Peninsula,  where winters are long and cold,  and summers are too

short. But every year now,    when winter sets in,  I look out of my window and think of the flowers I'll

see next spring in my little garden. I think about what my children did for me,    and I get tears in my eyes

every time.

     I'm still not sure that money grows on trees. But I know love does!

1. By saying "Do you see a money tree outside…"the mother actually means "________".

A. Observation is the best teacher

B. Seeing is believing

C. The outsider sees the most of the game

D. It is not easy to gain money

2. The best title for the passage would probably be "________".

A. My flower garden

B. Marvin helps to realize my dream

C. Love in Michigan

D. Money grows on trees

3. The underlined word "nofrills"in the fifth paragraph is similar in meaning to "________".

A. wasteful  

B. tight

C. absurd  

D. helpful

4. From the last three paragraphs we can infer that the mother is________.

A. divorced when she was young

B. not caring for her kids any longer

C. alone but not at all lonely

D. prouder with her garden than with her kids

单项选择题