试题与答案

设关系R与关系S具有相同的目(或称度),且相对应的属性的值取自同一个域,则R-(R-

题型:单项选择题

题目:

设关系R与关系S具有相同的目(或称度),且相对应的属性的值取自同一个域,则R-(R-S)等于( )。

A.R∪S

B.R∩S

C.R×S

D.R-S

答案:

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参考答案:D解析:党的决策领导,是指公安机关要及时向党委汇报重要的敌情、社情和治安情况,党委根据具体情况提出宏观性的决策意见,责成并督促政府和公安机关贯彻执行。

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题型:单项选择题

Many people acquire software programs for their home computers by illegally copying those programs rather than purchasing them. People who own home computers must be making, on average, fewer illegal copies of software programs than before, however, since the average number of software programs that people purchase to use on their home computers has increased substantially over the past five years.
Which of the following, if true, most strengthens the argument

A.The number of home computers in use has increased substantially over the past five years.

B.Five years ago, about half of the software programs used on home computers had been illegally copied rather than purchased.

C.Most people who have home computers use their computers more frequently the longer they have them.

D.Few people who prefer to copy computer software programs illegally cannot copy the software programs they want because they have no acquaintances who have those software programs.

E.(E) On average, people with home computers have the same number of software programs today as people with home computers did five years ago.

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