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【单选题】
关系数据模型是目前最重要的一种数据模型,它的三个组成要素分别是( )?A.
实体完整性、参照完整性、用户自定义完整性
B.
数据结构、数据操作、数据的完整性约束条件
C.
数据增加、数据修改、数据查询
D.
外模式、模式、内模式
拍照语音搜题，微信中搜索"皮皮学"使用
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举一反三
【单选题】Senator Smart, who understands economic principles, is trying to convince workers in her district that trade with other countries is beneficial. Senator Smart should argue that trade can be beneficial
A.
only if it allows us to obtain things that we couldn't make for ourselves.
B.
because it allows specialization, which increases total output.
C.
to us if we can gain and the others involved in the trade lose.
D.
in only a limited number of circumstances because others are typically self-interested.
【简答题】腹膜腔由__和__互相延续、移行,共同围成不规则的潜在性腔隙。
【简答题】旅游资源包括的范围很广，种类繁多，按照其形成的条件，可将旅游资源分为____旅游资源和人文旅游资源。
【单选题】It was a fixing sight: there, in the Capitol itself, a U.S. Senator often mocked for his halting, inarticulate speaking, reached deep into his Midwestern roots and spoke eloquently, even poetically, a...
A.
annoyed.
B.
amazed.
C.
agonized.
D.
agitated.
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