单项选择题

Let the schema R(U, F), U=ABCD, F={A→BC, C→D }. The schema R(U, F) is in the normal form of（）.

A．1NF
B．2NF
C．3NF
D．BCNF

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单项选择题

Which one of the following expressions is equivalent to 'X BETWEEN 15 AND 25'（）

A．X>15 AND X<25
B．X=15 AND X=25
C．X>25 AND X<15
D．X> = 15 AND X<=25

单项选择题

In the ISO 9126, there are six key software quality properties, including functionality, reliability, usability, efficiency, maintainability, as well as（）.

A．correctness
B．security
C．portability
D．stability

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