进行并、差、交集合运算的两个关系必须具有相同的 ______,即元组结构相同。

题型:填空题

问题:

进行并、差、交集合运算的两个关系必须具有相同的 ______,即元组结构相同。

考点:计算机等级考试数据库技术三级数据库技术笔试
题型:填空题

根据短文内容,按要求答题。

Dear Helen,

     This has already been a great trip and I haven't even left the airport yet! Even leaving Shanghai was

exciting. We went to Pudong (浦东) International Airport on the new super fast train. It travels at four

hundred and thirty kilometers per hour! Before the train line was built, it took a long time to get to the

airport by taxi or bus.

     We have quite a long time to wait here in Hong Kong before we fly to London tomorrow. In the old

Hong Kong airport only had a few small televisions, but the new airport has lots of super sized televisions

showing sport, comedy (喜剧) and music shows. The old airport only had a few shops selling newspapers

and books, but the new airport has shops selling all sorts of different things. The new airport hotel offers

many special service-including a foot massage (按摩) service! Dad said we can go there later to relax

(放松).

      There weren't many restaurants in the old airport, but it's hard to decide which restaurant to go to

in the new airport. There are so many different ones with food from all over the world. I left my bag in

a restaurant and I thought I lost it, but it was safe in the lost and found (失物招领处) house.

      The airport has a bus that can take you for a quick sightseeing and shopping tour of the city. I hope

you are well!

     See you soon!

1. How far does the new super fast train travel per hour?

___________________________________________________________

2. Where will the writer go tomorrow?

___________________________________________________________

3. The old Hong Kong airport had lots of super sized televisions, didn't it?

___________________________________________________________

4. Where did the writer find his bag?

___________________________________________________________

5. How can they go sightseeing and shopping?

___________________________________________________________

题型:填空题

在双氧水中加入少量的二氧化锰,双氧水的分解速率加大,但反应前后二氧化锰的化学性质和质量都没有改变,则二氧化锰对双氧水的分解起了_________作用,是________剂。

题型:填空题

电器工作时,发热和散热不同时存在于电器发热过程中。

题型:填空题

网络采购相比传统采购,优势主要体现在()

A.降低采购成本

B.促进采购信息化建设

C.减少人为干扰

D.有效保证采购质量

题型:填空题

油田水处理中使用的缓蚀剂按机理可分为()类。

A.2

B.3

C.4

D.5

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