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【单选题】
下列关于关系模式的码和外码的叙述中，( )是正确的 Ⅰ．主码可以是单个属性，也可以是属性组 Ⅱ．外码可以是单个属性，也可以是属性组 Ⅲ．一个关系模式的主码与该关系模式的任何一个外码的交一定为空 Ⅳ．一个关系模式的主码与该关系模式的所有外码一定包含了该关系模式的所有属性A.
Ⅰ和Ⅱ
B.
Ⅰ、Ⅱ和Ⅲ
C.
Ⅰ、Ⅱ和Ⅳ
D.
Ⅰ、Ⅲ和Ⅳ
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举一反三
【简答题】____ 是用竹紫或森素、铁素等为骨干相拼悬品起的大桥。多建于水流急、不易做桥墩的陡岸险谷,主耍见于西南地区。
【单选题】It takes an _________ of ten weeks for a house sale to be completed.
A.
on average
B.
averagely
C.
average
D.
averaged
【单选题】Plato was a superb writer, and his works are part of the world's great literature. Most of his existing work is _______ dialogs and letters.
A.
in the name of
B.
in the face of
C.
in the charge of
D.
in the form of
【简答题】Ten weeks _____ (be) needed to complete the task.
【单选题】Plato was a superb writer, and his works are part of the world's great lierature. Most of his existing work is ______ dialogs and letters.
A.
in the form of
B.
in the from of
C.
in the matter of
D.
in the detail
【单选题】Plato was a superb writer, and his works are part of the world’s great literature. Most of his existing work is ____ dialogs and letter.
A.
in the form of
B.
in terms of
C.
in the formation of
D.
in view of
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