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问题 单项选择题

下列关于SQL中的索引(Index)的叙述中，正确的是( )。

A．在主键上不能创建UNIQUE索引
B．一个基本表上可以创建多个聚簇索引
C．有时为了加快维护数据库的速度，应删除一些索引
D．删除索引时关于索引的描述仍会保留在数据字典中，供以后使用

答案

参考答案：C

填空题

根据句意及汉语提示，填写句中所缺的单词。

1. _______ (星期二) is the third day of a week, between Monday and Wednesday.

2. Bob was very careless, He made so many _______ (错误) that he failed the exam.

3. My mother always _______ (鼓励) me face to the difficulties bravely.

4. Our teacher are always all very _______ (严格) with us students in the study.

5. Last year we went to Egypt, but this summer we are going to visit an _______ (亚洲) country.

6. _______ (除……之外) singing English songs, there are any other fun ways to learn English.

7. We'll have a party next Saturday for Lily's _______ (二十) birthday.

8. Thanks to the _______ (政府), thousands of people in Wenchun have moved into their new houses.

9. I can't hear you _______ (清楚地), Could you please speak more slowly.

10. They invited me to the play, but I had to _______ (拒绝) because I was very busy.

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单项选择题

有关主起落架收放作动筒的描述最正确的是（）

A、仅用于收上起落架

B、收上起落架后作为侧撑杆

C、机械锁在收上位

D、以上全不正确
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