设有关系R和S,关系代数表达式R-(R-S)表示的是A.R∩S B.R-S C.R∪

题型:单项选择题

问题:

设有关系R和S,关系代数表达式R-(R-S)表示的是

A.R∩S

B.R-S

C.R∪S

D.R÷S

考点:计算机等级考试数据库技术三级数据库技术笔试24
题型:单项选择题

弘扬民族精神是历史影视的主题之一。下列再现了邓世昌英勇抗击日本侵略者的影片是( )。   

A.《鸦片战争》

B.《火烧圆明园》

C.《太平天国》

D.《甲午风云》

题型:单项选择题

A new ordinance passed by the Gorenton Council a year ago banned the sale of all nonrecyclable plastic packaging for food being sold in Gorenton. A substantial percentage of Gorenton’s plastic waste, however, is still composed of nonrecyclable plastic food packaging.
Which of the following, if true, best contributes to reconciling the apparent discrepancy above ?()

A.Fewer food products are packaged in nonrecyclable plasticstoday than were so packaged a year ago.

B.The new ordinance affects only plastic food packaging and not other products packaged in plastic, many of which are sold in Gorenton.

C.Grocery and other stores in nearby suburban areas patronized by many Gorenton residents are unaffected by the new ordinance.

D.Many food products formerly packaged in nonrecyclable plastics are now specially packaged in recyclable plastic before being shipped so that they can be sold in Gorenton.

E.The total amount of both Gorenton’s trash and its plastic waste grew considerably over the past year.

题型:单项选择题

帝王陵墓封土形制自商朝以来,经历了“覆斗方上”式、“因山为陵”式和“宝城宝顶”式的演化过程。

题型:单项选择题

水表完好率是运行正常的水表数与已装水表数的()。

A.和

B.差

C.积

D.比值

题型:单项选择题

在质量管理体系认证中,认证机构对申请单位的质量管理体系审核是质量管理体系认证的关键环节,其基本的工作程序是______。
①文件审核 ②现场审核 ③机构设置
④批准申请报告 ⑤提出审核报告

A.①②
B.①②③④
C.①②⑤
D.①③④

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