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【单选题】
The flight attendant welcomed us ___ the plane.A.
abroad
B.
aboard
C.
board
D.
broad
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举一反三
【简答题】关系模型中允许定义三种数据约束，它们是实体完整性约束、参照完整性约束和_________。
【简答题】关系模式的三类完整性约束条件分别是实体完整性、参照完整性约束和 ______。
【单选题】Why does the author say that it was the artists who kept the keys in Paragraph 6?
A.
To show that the artists play a very important role in lifting the souls of people and thus enabling people to have a pure life.
B.
To demonstrate that artists and their paintings should serve as a bridge between the universal mind and the mind of humans.
C.
To prove that artists were very important in expressing the themes of the Hudson River paintings.
D.
To state that artists should have a broad knowledge of the Bible in order to fully depict the themes of the Hudson River paintings.
【简答题】什么是实体完整性约束、参照完整性约束和用户定义的完整性约束(域完整性约束)?
【简答题】什么是实体完整性?可以通过哪些方法来实现实体完整性规则?
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